I believe "hij is een tolerant man" is also correct. Or is this too archaic?
It's fine, less common than tolerante, but I don't think it's very archaic (yet).
@all: the standard rules apply, there is just an extra form that is accepted as well, this is an exception (I don't have time now to look it up now, but I think it's for adjectives before nouns describing a person)
I wouldn't worry too much about it, unless you're an advanced student (and even then, I bet some native speakers aren't aware of the exception). You can just stick to the rules explained here, no problem: https://www.duolingo.com/comment/3888221