I have an OC who's canonically a maleherm but isn't often depicted with such assets, should I still tag my content with maleherm_(lore)?

Yep, the lore tags were implemented for this purpose specifically :)

generally, yes. that's what those tags are for.

the only time you wouldn't is when the character is supposed to be depicted off-canon (i.e. crossgender).

You also shouldn't tag maleherm_(lore) if the character is already tagged maleherm. The lore tags are only used when it doesn't match what's already tagged by TWYS.

Yes.