My question is as stated above - what is the expected behavior when I go into the server config and set primaryPartySystem to ftb_teams? I was under the impression that this would make it so that openpac would use the FTB claims system as its backend, but changing this setting seems to have done nothing?

I have set it to ftb_teams, but my claims from FTB Teams do not appear in the World Map or minimap, and the openpac claims I make from within the world map don't seem to register on FTB Teams' end.

FTB Teams does not add chunk claims, it adds a party system. This mod supports it by default, just like the built-in party system. The primaryPartySystem option is for cases where only 1 system can be used. I don't think it ever matters what you have it set to at the moment.