Totally agree. It's well worth working closely with your designer to make your interface work with nibs, not against them. Little things like putting button icons on the left side of the button and putting a 20px gutter between elements add up fast.
That's actually a good way to see if your designer knows how to create a design within the conventions of the platform. Violating too many of a NIBs conventions tends to mean either a game (not really going to use NIBs) or something that will be hard on the users.
