I set up one insurgency and an occupying force and it works just fine. I added an opposing faction's insurgency to the mission and the latter insurgency is no longer active. Is this by design or a misconfig on my part?

bump

Did you setup a second OPCOM that would be controlling the second insurgent force and link them to the BLUFOR objectives?

yessir, both insurgencies received an OPCOM. Force 1 worked fine. I added Force 2, different faction, but similar setup. Force 2 spawned and worked fine but Force 1 did not even spawn.

If it IS possible, it must be a misconfig on my part.

Yeah it sounds like you don't have something connecting properly. If they didn't spawn at all then you may not have the objectives connected properly but without seeing what you have it is difficult to diagnose.