I can totally see him using crack, but I'm skeptical of the stories told by the wife of his distant family member.
For all we know, they could be selling this story for personal gain. They could have heard bits and pieces from other family members then filled in the blanks incorrectly. They could be pissed at him and blatantly lying to get back at him.
Family members--especially distant family members / hangers-on--can be extremely frustrating. Especially if they disapprove of one's behavior. It's all too easy to cast aspersions on family with whom you're angry, disappointed, or jealous.
I think it's absurd of him to say he's "perfectly fine." His past likely contradicts that. If this is true, he should just own it. He went to rehab supposedly. What's the big deal if he did it in the past? Or really if he's still doing it. Everyone knows he uses drugs / alcohol.