If you completely crush the opposition, then there's no hostility to worry about.
[But that's not the point, is it?]
I still believe it would be beneficial to try to force them into working together. If it doesn't work, you simply have to withdraw one of them and replace it with another to finish the battle and you can figure out what to do from there. You have nothing to lose from trying it.
[VIDEO]
If you completely crush the opposition, then there's no hostility to worry about.
[But that's not the point, is it?]
I still believe it would be beneficial to try to force them into working together. If it doesn't work, you simply have to withdraw one of them and replace it with another to finish the battle and you can figure out what to do from there. You have nothing to lose from trying it.