The fact that the device requires IPv4 is a much different complaint than anything to do with the use of the DNS protocol. What if YouTube were just IPv4 only? Then you'd be in the same situation no matter what DNS server you are using.
Then DHCP isn't even used/required and this is all moot as clients are fully allowed (and even expected) to self-configure, including DNS if they want. Heck, DNS advertisement via IPv6-RA is still only even a proposed standard: https://tools.ietf.org/html/rfc6106 it hasn't been ratified yet, and support isn't widespread.