Spare tire for Aussie'd rear question....

I'm running 30x9.5x15" tires and have an 8.25 rear end with an Aussie locker in it on my 96 AW4, 231'd XJ..

I only have a 235/75/15 spare.
I can definitely run it for the fronts but is it okay to run it in the rear with an Aussie?

I wouldn't, little over an inch difference, always push a front to the rear and use the spare up front only.. and look for a 30x9.50

+1, i would pick up the right size spare or rotate tires if need be.