I'm pretty sure you can use knucks and such along with an unarmed strike. I'm also certain they're intended to stack with Critical Strike (Unarmed).
Shock Gloves are an unarmed weapon, but I wouldn't allow the powers to affect them simply because they, by design, simply replace your unarmed attack with a static thing. I might let Critical Strike affect them, but not Penetrating Strike, if only because it's established in the game's rules that when a weapon does electrical damage, you use a set AP of -5 (like stick and shock ammo, for instance) regardless of what the attack would normally be.
Also, you don't punch people with shock gloves, but you do with knucks. For the latter, it's the same kind of attack, uses the same skill, so on so forth.
A "melee weapon" doesn't specifically not include brass knuckles. It's still a weapon used in melee-- It's not using the term like a videogame would. It's just to illustrate that a weapon focus only helps if you hit them with the focus.