whether it's allowed or not is probably less pertinent than whether it'll get downvoted. I've never seen a flagged comment that was just "thanks", but I suspect I probably have seen a heavily downvoted one, although I can't think of a specific example
>>permo-+(OP)
That's why dang raises awareness that this is allowed, because most of the people (i guess) downvote because they think it is against the guidelines.