Take this as a lessened learned to inspect ALL of the RV when you drop it off and pick it up from any repair place. That being said, I haven't done it either. It's what we SHOULD do but don't. Of course, someone on this site will claim to do it though.
Now, do you really care about the skylight crack or are you just PO'ed that you didn't catch it? Anyway, stick some EB on it and be done with it. If that doesn't make you happy, replace it. You can't really go back to dealer if you didn't point it out AT the dealership. How does the dealer know what you did with it after you left?