Rousseau in the Social Contract demonstrated how "might is right" is an empty slogan because it leads to no rights at all.
One might be the stronger right now and impose their will, but as soon as they sleep, or are ill, or alone, they are bound to be backstabbed and be, in turn, like Caesar, the weaker because of circumstances. And no single individual is stronger than a determined mob. The "higher life form" will always be at the mercy of a group of "lesser ones". Does that make them higher? It seems this notion of highness in life form is ill defined.
To come back to Nietzsche, any person claiming to be an ubermensh with at least 2 brain cells should understand that they won't make it on their own. They still need some form of cooperation, a kind of gentleman agreement to not commit aggression against each other, wether those others are uber or regular.
Of course, being an ubermensh, they depend on no one's moral judgement. The rules to them is not sacred, abiding does not make them good nor breaking it make then evil (they are beyond those categories, as we know).
They accept the rules in so far as it is in their best interest, and know to opt out if turns out to be detrimental. Yet opting out can't be done lightly, otherwise there can be no agreement. This is the delicate balance the ubermensh knows to find. I'd even say it is the fact that they understand and can find this balance that makes them ubermensh.
I understand it might seem counter intuitive to describe an ubermensh abiding rules, but figure a true genius to the like of Beethoven: being an ubermensh means he realizes his full potential. Now, he can either willingly abide by a modicum of social rules to uphold society and be able to buy food, ink and paper at the shop next door and commit most of his time to composition, or reject all rules and spend his days as a hunter gatherer. Which of those life plans do you think most realizes his full potential?