I don't see how the dealer can say that with confidence. You don't want a 2" longer shock if you don't have a 2" longer spacer. You'd be better off going back to the stock rear shocks with a 1" spacer.
While I highly doubt you will have issues, the fact that your shocks will be 1" longer than the spring assembly will leave a 1" void on full-extension, so instead of the shock being your limiting suspension travel factor, your swaybar endlinks will be, and those ball joints in the endlinks will definitely pop with that much downward pressure. Now...I will say you'll probably never lift a wheel or get airborne on normal driving but anything is possible. They would also need to modify or remove the track bar extension with a 1" spacer. It's designed for a 2" lift and will move the axle (horizontally) out of alignment, and that would be no bueno for your thrust angle. Again i think you'd be better off with no trackbar extension on a 1" spacer.