I'm running 33x12.50-15 on stock TJ 15x8 rims on my YJ with no issues whatsoever. I ran 33x10.50-15 on my Comanche (MJ) on stock 15x7 Grizzly rims for 2 years, no rubbing. I also ran 34x9.50-15 Swampers on stock Steel 15x7 YJ rims on the MJ for off-roading, slight rubbing on full stuff, trimming took care of it.
I would not waste your money on spacers, for the price of 4 spacers you could buy a set of Rockcrawlers for about $100 more.
Sure try the 33's on stock rims but be prepared to adjust your steering stops to avoid rubbing on your LCA's if you are running an XJ, ZJ, MJ or TJ.