Sure, why not? Poly is as people describe it for themselves, with the general understanding that it involves multiple love and consent. If they haven't reached a point of being able to consent yet then they have some work to do.
I don't believe poly is based on hypocrisy. What is good for one is good for all, but sometimes it take doing some work to get there. Usually that work is around fear and threat of being replaced, not being good enough, not belonging, being abandoned or not being loved... Or all of the above and maybe more. If the person of which you speak is attempting to control others by setting rules that are meant to restrict, then I would be asking them if one of the above fears and/or threats is the reason and work toward solving that with them.
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