Yep, the A/V cables are the same. But when you use them, you might notice that the Nomad is a tad slower than the Genesis.
At least, that's what I noticed. Not with Streets of Rage, but with NFL 95, and other sports games.
But when you fire up Streets of Rage 2 (as I did repeatedly last weekend) you forget all that - there's nothing like playing it as a handheld.
There are two types of GG battery packs, from what I can tell, one is the actual packs that sit in the battery compartment, the other is this mouse looking thing that connects to the A/C Adaptor. Obviously the first won't work w/ the Nomad, but the 2nd is touted as working. (I'm sure it'd work w/ a lot of things)
That reminds me - up until this point I thought I didn't buy anything at a console launch, but I got the nomad the day it came out (what was that, 6 years ago?).