Can former Marines, now in the Army, wear a combat patch from their Marine deployment?

I was in the Marines for five years, deployed to Iraq, got out, did a few months in CIV DIV and came back into the Army. Some of my NCOs, some prior-Marines some not, tell me I can wear it. Others say no, unless I was in the Army attached to a Marine unit. Every board I go to I am asked why I have an Iraqi campaign medal but but no combat patch. Somebody please help me get a straight answer.