I've run across a player named Green light in the S W A T legion and he has no weapons and no defensive placements, but he is able to win in Pvp Matches, are these allowed???

It's possable and allowed. Just a differant way of doing things.

You can increase your attack and defence stats by putting rank points into Tactical Officers and Helmsmen. Thier are also artifacts which will increase the ammount of hull and shields a ship can have without any modules. He might be running a small ship build to limit the damage he takes. without more info I can't say for sure but its certainly possable to win fights without any ship modules.