I'm assuming you could also do this with hard wood insert. Something like Ipe or cocobolo?
Yes, no problem. I've done it with padauk, purpleheart, cocbolo, ebony and bloodwood. Works great, looks good, and is easier than horn.
The green & white arrows have purpleheart inserts, and the red & black have cocobolo.
I normally cut my inserts 1.5" deep on arrows for target weight bows, and the standard 2" deep for warbow weight. The difference in weight between the insert material and the wood you remove to insert it is negligible. No balance issues. It's much less than the weight of a plastic nock.