Just tested this with Suigetsu and TenTen. 2* Haku does indeed seem to not buff water ninjas. In fact the animation for the buff plays but the text (Attack^ // Ninjutsu ^) Does not show up. The damage does not change either. The reason I tested both tenten and suigetsu is because I thought there might be an issue with the double scaling of suigetsu (nin/tai) but since tenten is pure tai that's debunked.

PS: I just upgraded my Haku to 3*s and it does seem that 3* haku DOES NOT have this issue.
In short: 2* Haku's barrier does not apply a buff to water ninjas while 3* does. I would imagine this is intended and there is possible a translation/text error.
This post was last edited by RiusSensei at 2016-8-17 06:32

Haku is actually VERY powerful. In exchange for not being able to finish off opponents he applies Accupuncture on Crit and deals 40% bonus damage BY DEFAULT.

The drawback is easily overcome by simply not having your combo end with haku =)