An amicus brief can support the arguments of one party or the other, or be entirely neutral and support neither party. In general, an amicus is not supposed to be a person with a direct interest in the outcome of the specific case. Nick doesn't have such a direct interest, but he is hardly the sort of disinterested party trying to help the court with a thorny issue of law. He is clearly, for his own reasons, an advocate of one side, and has at least an indirect interest in the outcome of the specific case.
So long as he keeps it to the specific legal issue or issues it's about, I don't see how it can cause much harm. I'm jut not a huge fan of amicus briefs in general and don't think any but the very best of them are actually helpful to the court.