They're not related near as I can figure. Orbit is from orbis, ring, circle; obiter means in passing as has been said before. Can't trace orbis past Latin nor could I find any details about obiter although I suspect some connection to it as the 3rd person singular of the verb ire, to go.


Quick edit: Seems to be no verb obire. There is a preposition ob meaning in front of, before; in return for; because of, on account of.