Heck, I've used yarn, antron, cdc puffs, and foam.
I haven't tried hairs like dear or elk, was afraid that wrapping a thread base on the hair would cause too much flair and make it harder than it's worth to wrap a feather around! It might be easiear without a thread base though.
Using buck tail is certainly ok. I try to even the tips as best I can though. That's the only way to control the height of the post without clipping the hair. But even that's ok, yarn and foam are clipped. Why not hair?!

Charlie