Yes, the kernel included in PVE 6 is newer and has even better support for Ryzen/Threadripper CPUs. Internally we are using some EPYC servers for testing, and they are working wonderfully.
As far as I can tell, even PCIe passthrough is working without issues now on Threadripper/EPYC.
Yes, Threadripper is supported by Proxmox.
The only thing known to be tricky (though not impossible) with these CPUs is PCI(e) passthrough. If you don't need that, you're fine.