Ser ut som en älg. Luktar som en älg. Smakar som en älg. Ja. Det är definitivt en älg.
Det is just a formal subject here. It doesn't take the gender of the object/animal/person in question. It's like saying "The (previously unknown or unspecified) something or someone is a moose". I think it would be a different matter, though, if in the sentence before, the moose was already mentioned, e.g.: Titta, en älg! Den äter gräs! In this case, den can refer back to älg, therefore it has to be utrum.
As for definitivt: Appending the -t has got nothing to do with älg being neutrum or utrum, it's just that you have to use the adverb form of definitiv (similar to definitely in English).