TUCK

Can I tuck a 20" 8.5 with a +30 offset on a 99 Frontier

anything is possible!!!

The rim has no lip it looks like a FWD rim.

I dont think so

you need at least a +40 and it will still be way close. a +45 is even better, but good luck finding either in a 6 lug.

anything is possible, but possible could mean having to build new control arms...