Speaking from experience.
31's on aftermarket wheels are possible without a lift.
31's on aftermarket wheels with TJ flares (with the required trimming) are perfect.
30's on stock wheels, stock fenders is a good setup if you dont want any issues.
I ran 31x10.5's on AR aluminum wheels on my old 92 until i lifted it and got 33's. That was stock flares. I did the lift and tires only a month or two after i got it though. The PO had the 31's on it when i bought it.
I ran 30x9.5's on stock aluminum wheels on my 1990 for almost the entire time I owned it. I had to extend the steering stops to keep them from contacting the springs at full lock, but otherwise, perfect fit.
My 92 with 31's before i lifted it.