[GodBeastX]

This might sound odd to do, but I would model it with Enemy disadvantage coupled in. Roll against Ally to summon. Roll against enemy to make them hostile or friendly.

Edit:

Oh wait, I see what you're saying. You mean raise an NPC that is effectively neutral or will attack everyone... the option above might still apply for pricing it. You could build the Ally advantage then build enemy along side it and find the difference in cost to fund it.

Though in general, looking at something like infectious bites, if something isn't ally or enemy inherently, or offers no real exploitable advantage, it becomes 0 points. It's almost like how a species that can give birth to more of themselves is worth 0 points because more NPCs isn't necessarily an advantage.

It's hard to say really.