A scope with very long eye relief might mount in front of the rear sight but I haven't tried this.
Then you run into mounting problems since the rail is so short. You get enough eye relief and you only have room for one ring. I tried it with a few different scopes, but then lost interest in putting optics on it, so I havent toyed with it a lot.
The rail is too tall to mount a red dot on, well, you can mount the red dot but it blocks the iron sights. I bought my upper from ADCOFirearms.com and got the tac handle instead of the standard carry handle because I thought it would give me a little more flexabilty, and it was five bucks cheaper IIRC. Now that I have it, I dont care for it. I think I may actually have more options for mounting a scope with a standard carry handle. If the rail was longer would be better IMO, they do sell and extended rail however it didn't have a rear sight last time I looked. With the scout rail that has iron sights you get a full-length rail that runs over the handgaurd and mounts to a weaver gas block up front, I dont care much for that idea either mainly because of the way it looks. Luckily since mine is an A3 I can change my mind easily, however with the A2 UTE upper you dont have that option.
If I were to do it again I'd probably go with a standard carry handle or a
Bushmaster A3 rear sight, or a simular one that will leave the rest of the rail exposed, I may wind up doing that to my carbine anyway, but at the moment I dont have any optics planned for it. I do plan on another A3 (9mm) in the future, and I plan on using an A1 or A2 rear sight simular to the BM sight linked above.
As I said, I havent toys with it a lot, and I'm sure I could figure something out if I was determined enough. I'm just not that determined.