For viera, honestly just do what you do for au'ra and full helms... just have them clip though. Like seriously the giant horn types for the au'ra realistically should mean they can't use a helm since even if you had horn holes in the sides, how would you explain getting the rest of the horn through that small hole?

Only people who want to whine about something would care that hats or helms didn't physically show ear slots, everyone else would be 100% okay with them just clipping through cause they already do that for au'ra! And I haven't seen anyone myself complain about it.

Hrothgar? for helms I kinda get it like full on full knight like helms I mean you could make their helms look like they are made specially to show the beast like face... but I don't think anyone would mind if you just had the helm cover the head like any other race because if people didn't like that the helms didn't mold perfectly to match their beast face? They wouldn't use it anyway while the people who just want to use helms would, hats? Do the same thing for miqo'te, have the ears just clip through the hat.