Short version - buy a QD AR mount, get folding back up sights, and be merry. It'll all work together.
I will probably call the number on their website and see if it gives me a menu option for Tech Support. I prefer to use email as that lets me print out the information for future use.
Call the number above, option 2 gets you to tech support. The recording before the options lists directs you to the Bushnell website also (bushnell owns Simmons). At the top of the Bushnell.com page, just left of center is "Service & Support." The subsequent page offers the same phone numbers as I posted above, preceded by a link which says, "Contact us" in orange font. Clicking there, you're carried to a page with "by phone," "if you would prefer to write us, send a letter to:," and "Use the form below to send us an email."
So without looking very hard, I googled "Simmons optics." I found the customer support number I copied above. Calling that number, a 25 second call directed me to the Bushnell site, and two clicks later, I had the email form you seek... Bushnell handles all customer service and support issues for Simmons optics.
Looking a little more deeply, meaning I spent about 5min of casual googling while I was listening to babbling on a conference call - I searched "height of Magpul BUIS folded" and found 0.51". I looked at midwayusa.com for the height of the Burris PEPR and found 1" from rail to ring. Also at midway, I noted the Simmons 44mag optics all have 38mm eyebox diameters. For a 1" tube (25.4mm), that's 6.3mm of eyebox hang below the bottom of the tube - aka 0.248". S0, the gap between the bottom of the tube and the rail is 1", the eyebox hangs down ~0.25", and the sight sticks up 0.5" - you should have just under 1/4" of clearance between the magpul BUIS and the eyebox of your Simmons 44mag optic.
The Simmons 44mag scope isn't that big of a scope, in the scheme of things. The eyebox is 4mm smaller diameter than the Bushnell Elite 6500 2.5-16x50mm pictured here, 5 smaller than the NF NXS 5.5-22x56 my wife is running on her coyote AR and the 4-16x44mm Sig Tango4 I'm running on my gas gun match rifle, and 6mm smaller than the Bushnell AR 3-9x (also pictured here). Magpul polymer BUIS fit under ALL of the optics listed above - so using a Simmons 44 Mag optic and a standard AR height ring or mount, you will have no problem getting the folding rear sights to fit beneath the eyebox. You will, however, either need a QD mount, like the QD Burris PEPR pictured on the assembled rifle below, or a means to remove the mount.For example: on that 18" upper below, if I want to remove the optic with a folding rear sight behind it, I'd have to slide the mount clear off of the front of the handguard - not exactly QD - whereas the QD PEPR optic mounted on the complete 22" rifle pops of quickly with two throw levers and a quick tip.
These optics below are set up for hunting with the stock extended - not intended to be fired with my nose on the charging handle. Moving the optic forward with my nose on the handle, I'd have even more room for the back up sights on the rail - but as you can see, there's ample room left behind the mounts to insert the folding rear sight.
