I think Leper Gnomes are the only non-Undead members we’ve seen in person. But it’s always been a sort of presumed factor of the Forsaken. That they’re not just for dead Lordaeronians, but anyone who has been plagued and/or scorned by the world they knew.
The only pre-requisite to joining the Forsaken was proving your loyalty and swearing your fealty. The Forsaken are unique in this way. Their diversity. It’s a real shame it doesn’t get portrayed more often.
There’s oodles of potential there.