while i def prefer a 12.50 on 10" rim, the 31s dont look HORRIBLE. my jeep came with an off brand 31x10.50 on the stockers when i bought it and i had 15x10 with 5" bs in the garage from the old wrangler, i tossed them on, looks better than it did stock and while i definitely wouldnt air down, i've had no problems with popping a bead or getting a flat or anything crazy.
cliffs notes - while i wouldnt BUY 15x10s for 31s, if you already had them it would be a different story...