I use VYOS as a core router for my home network. I was configuring DHCP relay for a few subnets and never could get it to work until I came across the below link. So I ended up having to configure a relay on a subnet that actually has a dchp server. I know this is broken behavior. So with that said what types of problems can this cause by having a relay on the same subnet as the actual dhcp server? I might end up using my PFsense box to do the dhcp relaying until this is fixed.
I haven’t noticed any issues in my case, but if you wanted to ensure there was no problem, you could configure a firewall rule that dropped DHCP requests ingress on the DHCP server sgement, and ensure you are accepting DHCP replies from the DHCP server.