(someone who went on rabbit hole trip through tsnet) It's not very visible (and not really user-accessible) but Tailscale supports connecting arbitrary wireguard peers into the network, and it's how mullvad integration works IIRC - got confirmation on twitter I think from apenwarr.
So yes, tailscale is compatible with wireguard, it's just not exposed by any of the major coordination servers other than mullvad integration in tailscale.com, but the clients will happily consume information about wireguard peers that do not run tailscale at all.
So yes, tailscale is compatible with wireguard, it's just not exposed by any of the major coordination servers other than mullvad integration in tailscale.com, but the clients will happily consume information about wireguard peers that do not run tailscale at all.