On the OP's question: The main reason you don't see much with PCC s/SMGs that's specific to them, is form factor wise they have largely moved to something very similar to carbines. Additionally most strive to have the same manual of arms. Older SMG's like the UZI, MP5, Sten, etc all feature unique manuals of arms that you had to train for. Sort of like the SMLE and the M1, both are rifles, but with very different ways of fighting with them. With the SMG/PPC world approaching singularity with either the AR or AK platform, there's no real need to have different techniques than what works with carbines. Yes there are things like the MP-7, P90, and Kris Vector, but theses are a lot rarer than the legion of PCC's the mimic the AR/AK platform these days.
Also as a community the mil/LE/Comp shooters have stolen a lot from each other, and honestly there's a lot of overlap across all three areas. You'll see comp guys run the guns faster as their target discrimination is done on static targets with static target discrimination criterion. You'll see fingers stay on triggers as they sweep across no-shoots, and the muzzles stay's below the berm top and in the 180. Mil/LE tend to shoot a little more deliberately (the penalties for hitting a no-shot are a lot higher), but once the engagement starts, you'll see a lot more than 2-alpha hits (we trained for a long time to expect at least a half mag per target regardless of the weapon type). I could go on, but you get the idea.
In short the modern sub gun technique has really married into the modern carbine technique. Legacy sub gun designs, do have their own unique quirks due to the manual of arms (H&K slap anyone?) and require training around them. With a 3+ second reload on the Uzi, you need to be good on your transitions. If you're running 9mm in both guns, what do you gain what do you lose? Gun fighting is all about the fighting part, the gun just happens to be the tool we brought to the fight.
i'm just thinking about how i would approach 3gun style stages with a smg, which is close to PCC but not exactly. i'm just wondering what my splits and transitions will be like using the sling vs a brace or stock, etc.
One interesting question for a three gun/two gun match would be to require say 5-10 hits on a target. Does running in FA, burst, or SA work best for that balance of speed and accuracy? I'd hazard an extended stock regardless of the trigger option would provide the best accuracy. I learned the H&K sling technique for the MP5K, and it does work at the distance the K was designed for. Given the option however I'll take a full stock on even the K (the side folder works very well to keep it small until you need to go loud).
And on FA fire in LE, and the MP5 in specific:
The main reason that so many SWAT teams for so many years have had a FA capability was because they could. The MP5 was THE gun of choice for many years mainly due to HK's good marketing. A FA MP5 is the same price as an SA only one (for agencies), and it was normally articulated to the brass that you needed to be able to put more of those pistol caliber rounds on target fast. In the MP5's defense on FA, it will put an entire magazine in a 3" circle at 7yds with a mag dump. It will do about a 2" circle in quick 2-3 round bursts. You can take an extra second or so and put 30 rounds into a 1" dot at 7yds semi-auto. Most agencies ran them on FA and trained to put the sight COM and hold the trigger tell the bad guy fell, due to the intrinsic accuracy and controllability of the weapon. Just prior to the shift in LE to the AR platform most places had gone to SA fire, with a failure drill mindset as there were several cases of offenders taking long burst and not going down due to drugs or body armor. The shift was felt to be more of a tactical decision regarding the need to address a changing level of threat then against the usage of FA.
The AR platform never has been a FA platform for a number of reasons one was control, as it is much less controllable in FA then SA fire (especially compared to the MP5). A FA AR can keep all of it's rounds at 7 yds in a 4-5" circle on a FA mag dump, going to 2-3 rd bursts don't change that much. SA however can stack them on a 1" dot in a few seconds. The next was the higher lethality of the round compared to the MP5's 9mm (I'm talking 55gr Winchester Ranger XT SP's vs Gold Dot 9mm, not M855 Green tip vs. 9m ball), kept anyone from advocating a need to put half a magazine into a target like they had with the MP5. By this point in SWAT/LE liability had become the overriding concern for most agencies and being able to engage in precision fire with each round aimed sounds much better in court.
In a civilian context, the need is for the weapon to provide the capability for fire that strikes the target in an area that will lead to rapid incapacitation to cause a cessation of the threat. The fastest way to achieve this is to have a weapon capable of utilizing aimed precision fire to deliver all rounds to these target areas. If a FA weapon is a capable of maintaining that standard of accuracy I don't see it as a detriment in terms of the gunfight. I don't see it as having any more utility then a SA either though. As civilians we don't have the need to break contact or use suppression fire to fix and flank a target.
I'd say that with a weapon with minimal recoil (MP5, P-90, etc.) FA is not a disadvantage. The ability to control the weapon and still have acceptable accuracy even with a FA mag dump, allows the shooter to avoid stray rounds and put hits on the target. However a larger caliber weapon fired SA can put more powerful rounds (possibly with a higher amount of energy, bullet weight etc in one bullet then a burst of smaller rounds) into a target as/more accurately almost as fast. The choice becomes then which provides faster incapacitation and which lets you stretch your ammo further.
I will admit for stopping a vehicle I would prefer FA, in the form of a M2 .50 or a possibly a MK19 40mm grenade launcher.