Proxy ARP it's a thing and it is exactly what you've described :)
And if by proxy DNS you mean you'll subvert ARP to reach a DNS server... that's proxy ARP. DNS is a few layers above :)
Definition:
Proxy ARP is the technique in which one host, usually a router, answers ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination.
And if by proxy DNS you mean you'll subvert ARP to reach a DNS server... that's proxy ARP. DNS is a few layers above :)
Definition:
Proxy ARP is the technique in which one host, usually a router, answers ARP requests intended for another machine. By "faking" its identity, the router accepts responsibility for routing packets to the "real" destination.