Mata Hari and Piper

Vampire who plays piper, recruits the ally in question.

In order to recruit a nephandus, the vampire needs to be anti-tremere.

If Mata Hari would recruit a nephandus via piper, she doesn't count as anti-tremere for nephandus since Mata Hari is not playing the nephandus from your hand. Therefore it doesn't work.

This is decently straightforward imo..