I'm not sure I completely understanding your reply, but does this make sense:
So normally of course the verb implies the subject and sometimes there is a noun for that subject and sometimes not; besides other pronoun words, like Ego, etc, there is usually a noun for the subject when the verb is in the 3rd person. But here does Omnes, being an adjective, qualifies the "you" that is implied in the verb contemnitis? I think that makes sense of it.
One reason why I've enjoyed, for the most part, going through Familia Romana to learn to read Latin is because it gives you a chance to practice seeing the constructions in action, so to speak, but I don't think I've seen this one nor the appositive that you pointed out (which is now quite clear, hindsight being 20/20).
I still don't quite understand "Servus" in "servus factus sim." This doesn't seem to be another appositive, nor is it an adj, nor a predicate nominative for that matter, but it seems to be a direct object. Hence, I would have expected "servum."