At first blush, it shouldn't impact your web server in any way.
I haven't tried it, or I'd give an empirical answer, but the two should run just fine on the same server - assuming the server has the resources to handle it.
To use Pi-hole, you swap your DNS (or change your DHCP) and that *should* run independent of your web server.
Should...
Unless, of course, you configure Pi-hole to block your server. If you do that, then it will obviously block access.