Off roles in def tactics affect GR
 

How is the defense rating of a player impacted when he's stuck with an offensive role in the defense tactics?
(And why am I not allowed to give all players defense roles in some defensive tactical schemes?)

Even if you're playing Offensive, there's still a defensive role to every players game. And the reason I believe is because you don't want every player doing the exact same thing. One role starts cancelling out another depending on what role is taken.

I've a winger who's defensive role has to be set at Dangler, Speedy Forward, Sniper, etc. His DR rating is 48. Is it so low because he's not being asked to play defense and I shouldn't really worry about it?

As to the second part. He's got decent defensive ratings. He can throw a check, so it's not as if he's a total one way player. It'd be nice for him to check every once in awhile, but according to the manual, when he's assigned this role, he's told to just wait for an offensive opportunity, which I find kind of odd that you would tell someone NOT to check, if he's capable of it. I can understand if he's a all offense no defense, but this guy is capable.