Arch bubbling is common and neither proof the rest of the underneath is a rusty mess or absolutely fine - you really need to see underneath it to make that kind of assessment. I'd take a rusty arch one with FSH over a clean one with no history. It's been a some years since I owned a 350z now, but if I was buying one again, I'd arrange for it to be up on hoist before buying.
Good luck, they are awesome cars if you're patient and pick wisely.