This is a difficult question to answer. On one hand, I wouldn't feel right in offering someone something that I knew would contribute to a health problem, but at the same time, it wouldn't be my business to decide how someone goes about dealing with their problems.
I think it matters if the addiction is recognized medically or not. For instance, I could have a friend that in my own opinion drinks too much, but that doesn't necessarily make them an alcoholic. As a friend, I might try to suggest that we do things together that doesn't lend well to drinking (like going for hikes vs going out to a bar), but I don't think that I would not offer them a drink if they were at a party in my home...especially based on my own opinion of whether or not they have a drinking problem. Totally different if the drinking was a big enough problem that they had to seek professional help or were putting themselves in danger. In that case, I wouldn't want to enable and I might not invite them to any event where there would be drinking.
For the hoarding thing, I think Friend A's motivation needs to be considered. Did he offer the tv because it was a simple way to get rid of something and he dumped it on someone with a known problem, or is it just his opinion that Friend B is a hoarder? I've been to a lot of packed and messy homes, but I don't think that automatically makes someone a hoarder. I would be careful to not pass judgement on another adult simply because of my own biases and opinions.
If I knew for a fact that Friend B was indeed a hoarder and that their living conditions were unsafe and unhealthy and/or if Friend B was actively trying to get help for a hoarding problem, then no, I would not offer them anything or help add to their stash. If on the other hand, I had a personal opinion that they have too much stuff and too many tv's and I offered up a free one to which they said they'd take, then I'd give to them. Treating them no different than friends whose homes I find neater and less cluttered.
ETA: I re-read the OP and realized that it was the friend that helped move the TV that concluded that Friend B was a hoarder. I'm assuming that this friend does not know Friend B on any level, just made the assumption while visiting the house. And while the assumption may have been accurate, it could very well have not been. Like a said, cluttered, overstuffed, and dirty doesn't necessarily mean a hoarder. There is no evidence that Friend A maliciously or even selfishly used Friend B to get rid of a tv knowing that he had a problem. It's quite possible that Friend A had never even been to Friend B's home before he delivered the TV. I think in this particular case, it is no one's business. But, for the generic question, the above still stands for me. I might not offer something based on my opinion, but I wouldn't stop them from getting it unless I knew they had a medical condition or I felt they were in danger.