I think it was supposed to be 'over a Linux one'

UNIX only has maybe support [if you're thinking Solaris because if you're thinking SCO you might as well rot in a dark, cold and lonely place] that could excell although there are plenty of commercial offerings for Linux support nowadays [RedHat and Novell/SUSE anyone? ]

Solaris is made for SPARC [despite Sol x86 and OpenSolaris, that's it's main arch] so it will work flawlessly on those systems. Sometimes that kind of a union between OS and hardware is hard to find [Apple had it for desktops but now they're switching to x86 so there might be some issues there, we'll see]

As for the first question I'm thinking, obviously, ext2 and ext3 as well since those are the 'original' Linux filesystems [but if that question is actually worded like that from the interviewer than your brother should consider finding a different place of employment].

Yes, the only difference as already pointed out is that ext3 is journaled. All other technical details are the same [and for some interesting facts in general and a bit of history: http://en.wikipedia.org/wiki/Comparison_of_file_systems]

Cheers!