I've got a Raspberry Pi4 running Wireguard. I want to install Pi-Hole to this same RaspPi but for use for all clients on my network, not just those connecting via Wireguard. Is it OK to just install Pi-Hole and set it up as normal before point the DHCP server to the RaspPi's IP address? All the info I can find on the Net assume that you're using PiHole exclusively for Wireguard. TIA.
I run my WireGuard server and ad blocking server (AdGuard Home, I don't use PiHole any more) on separate machines. However, I can't see a reason why they wouldn't coexist. WireGuard is just another Linux network interface, it's literally designed that way. Unlike, say, OpenVPN with a TUN/TAP adapter, wg 'interfaces' baked in to the kernel networking stack and act just like any other network card in your machine. There's nothing special 'on top'.
You can add, modify and remove them just like any other (eg
ip link del wg0). That means you can also route and configure them just like any ordinary interface, too.
Once you have PiHole set up and WireGuard installed and configured, about the only special step I can think you may need is to allow the WG static network to query the PiHole instance. For example if your own physical LAN is 192.168.0.0/24 and WireGuard is issuing IPs in the 10.50.0.0/24 range then you
may have to configure PiHole to accept/listen on both those networks. That should be a simple step in the PiHole GUI.
That said, once the traffic/clients have arrived on your network via the Pi they should ordinarily be treated like any other LAN traffic. For example if I SSH into my home via WG, with a static IP on the wg0 interface of 10.0.0.2 I can still ping, connect to and otherwise interact with stuff on my LAN (10.100.0.0/24).
I've had WG and AGH running on my x86 router together in the past and didn't have issues, and I can't envisage you would either (aside from the considerations listed).