DHCP would be a great feature for Whonix-Gateway. Whether it is safe, or not safe, or can be made safe is unknown. Requires original research. The open question is, does DHCP have a feature, like “please tell me the IP address of you upstream router”?
Adding a DHCP daemon to the whonix internal network is not a good idea, if thats what you mean. It has a large attack surface and from what I saw on the subject, can almost certainly be an attack vector. I know that the internal networking in KVM has its own emulated DHCP routing, not sure about VirtualBox though.
May you please provide some more specific information here (if available to you)? Thanks!