Why not:

    return o2.compareTo(o1);

because the o2 vs o1 is easy to miss, while the -1 makes it obvious i'm intentionally reversing. my .02

Not if you give them more descriptive names

No, you can't. In particular -1 * Integer.MIN_VALUE == Integer.MIN_VALUE.

That would probably never matter in practice, though—I've rarely seen compareTo() return anything other than -1, 0, or 1; certainly never anything approaching MAX/MIN_VALUE. Still, bravo for considering all of the edge cases.