I got Endless Legends on Steam yesterday and bought all DLCs except for the OST. However, the Store page alludes to an Emperor Edition and Frozen Fangs content, but these are not reflected in the list of DLCs purchasable. Is this intended? Is this going to get fixed?

It should be included in base package now. Check if you see it available in-game, main menu - content management - expansions.

It isn't.

Whenever I try to add Frozen Fangs, I get redirected to my Steam's Store page. These are the additional content available.

Ditto and adding the free updates does jack squat

Yes, we've confirmed that there are indeed problems accessing Frozen Fangs, and have identified some potential causes. We're working on resolving the problem.