No servants, or worshippers, of the many-faced god once everyone is a mindless zombie. But from what we have so far, no, nada, zero chance, zilch. Which is not to say that is impossible for GRRM. We'd need to learn a lot of new things about the Others for that to change. Thus, I can't seem them in any way as 'allied' to the Others - creatures who apparently hate and appear to wish to destroy all living things with hot blood. They target specific people, and see death as a gift in certain circumstance, not as a universal need, prematurely. They are not a death cult dedicated to destroying all humanity. The gift of death from the many faced god does end misery etc - for those in that state. Some even speculate that Euron paid them a dragon's egg to kill Balon. The Faceless Men are already poking around the Citadel. They aren't just neutral actors in all of this. At some point the Faceless Men will get involved.
I can just rephrase the questions as Do you think the Faceless Men will be for or against the Others? Even if the Others don't cross the sea, their return threatens to upend the entire world order.
