Although everyone else may jump on the wagon of yea or nay, I really have no information on which to make a judgement. And neither do they.
I do not know whether his mashpia or mashpiim or shluchim he looked up to simply made a mistake, or they weighed dutifully their knowledge of his character and decided that his singing may lead him off, or his not being allowed to perform may lead him off.
I do not know whether the Shluchim who invited him to sing for them were relying on the judgement of his mentors, or simply didn't care. Knowing most of them, I think they relied on the judgement of his mentors. But I haven't asked them - how can I have an opinion?
What I see is that he has moved from strictly Lubavitcher notions in his songs, to Jewish notions, to universal notions - but still influenced by Yiddishkeit. He has not to my knowledge written or sung lyrics not in the spirit of Yiddishkeit. He has said that he moved from Chabad minhogim to general Jewish undefined Torah observance - which is still fine.
In fact, most Shluchim may now see this is an opportunity...
All I can truly say is, may Hashem bring a spirit upon him to protect him from completely losing his place.
The only lesson I can learn in truth, is to not voice opinions and condemnations when you have very little knowledge.
