Their twitter is private and only accessable by direct messaging them on furaffinity to get the link. They have made it clear that they do not want their work to be reposted anywhere and a bunch of their stuff has been leaked here recently. I don't know how artists get added to DNP so I don't know if they need to give their approval directly but it's clear they aren't happy with their stuff being leaked.

The artist themselves will have to submit a takedown request, and add that they want to be added to the DNP list. More info here.