I currently use the Wireguard client on a DD-WRT router to connect to a Wireguard server but I am looking at replacing this with a Tailscale setup. Is it possible to have some devices connect via a regular Wireguard client or will only the Tailscale client work?
The most common way to interoperate is via IP routing: make sure the Wireguard tunnels use a different set of IP prefixes from Tailscale. As Tailscale uses 100.64/10, using 10.0.0.0/8 for Wireguard is a common choice.
The Linux routing table will handle it from there.