As far as no diplomatic ship screwing up the Borg AI to be honest I really dont know how it is effecting them. I do know that among other things in the diplomacy aspect we did for the Borg it will cause them to ally with no one. Which is exactly what we want. We can accept a little AI bugginess for that. As long as there is nothing game breaking going on. The AI will build, and expand even if they have no diplomatic ships.
No, the Borg would never have allies...
I'm about 2 hours into a modified version of Whirlwind, it's 7 vs. me.
I'm the Borg, vs 2 Klink, 2 Rom, 2 Dom & 1 Fed, all allied as team 2 and set to Vicious. So far this has been a real fun fight, and I've almost lost twice now. If the attacks were a little more coordinated the AI may have beaten me, and I'm thinking it's gonna get really hairy later.
Anyway, the teams are locked, but I took down a fed diplomat ship ship before I saved and exited to make some dinner, so I know the AI is using them. I'm not sure what would happen if I unlocked the teams, but so far no crashes.