It depends on the ovpn files, the scripts will check if ‘dev tap’ is existed, then do the following steps. No changes with Openvpn Client UI.
I am not very clear about your question but I will try to answer.
In the server I create a ‘VPN’ network interface that uses tap0, then add dhcp:
Default LAN:
So when you set the dhcp you need to choose a network interface to assign the IPs, I am not sure which interface you want to use when you set the additional dhcp. Normally we don’t add two dhcp for a single interface.