Patch it in and/or copy/paste the perk tree into Hearthfire?
What I mean is it seems like an odd programming decision.
Dawnguard CANNOT reference Hearthfire and vice-versa, and DLCs can't be patched, iirc. DLC "patches" they've done in the past have been re-releasing the thing entirely. The Pitt was re-released iirc, and Honest Hearts caused problems since it couldn't be started without dismissing your companions first, and ED-E had a habit of getting lost in an elevator. Rather than re-release the entire DLC, they opted to patch in a terminal to the base-game that would force companions to dismiss; they did this BECAUSE DLC couldn't be patched.
To make it work, there'd have to be a second perk tree specific to being a werebear, which seems odd. Imagine scrolling through skills and seeing "Lycanthropy" and "Lycanthropy Jr."
To me that says they either won't implement werebears at all, haven't really thought this through OR werebears will be given traits that make them unique from werewolves. (though again, it still seems odd to give the current perk tree a general name like "Lycanthropy," if that's the case)