If I take my men as a reference here, I won't say that any of them is feeling something like compersion (for me translates to "being happy that I am with the other"). They are generally happy that I am happy but that hasn't got anything to do with my other relationship for them. We are stable, they accept and respect the other and we get along well.
I don't think it is neccessary to be happy about the other partner(s) or relationship(s) the partner has. You have to be OK with them and maybe be on friendly terms with your metamours but that's it. Compersion is some kind of bonus from my point of view. Nice to have (obviously) but not mandatory.
We aren't that long in a poly configuration (one year and some months), maybe this will change with time, but compersion was never a topic in our case.
Facts: 30, female, bi, v-type relationship with Sward (husband, straight, mono) and Lin (boyfriend, straight, mono), poly-fi and co-primary.