I'm creating a follower with a custom race and voice, but it seems that unless I give the npc a vanilla voice, then follower dialogue won't show up at all. Is there any way to have both a custom voice and follower dialogue?

You would need to add the custom voice to the follower FormList.

...I think.

Rats. I've heard of the FormList term, but I haven't gotten that deep into modding to know what it is.