It's Yes.

You can use the arrivals Fast Track Immigration queue (or security queue if transiting). It's been officially open to other airline *G for a couple of years now and was more or less unofficially available long before that. I was always allowed into the Fast Track queue as a UA *G since my first time in Turkey about 6 years ago. I believe TK officially changed it when *A implemented the Gold Track system.

The only thing at IST that is off limits to other airline *G is the direct entrance to the lounge from the check in area. For that you have to be in TK Business Class or TK Elite Plus.