Correct, You would have to ally with them as an Ultramarines detachment. But I do like the list. Just make sure to pick your fights with the command squad, they can still die to enough concentrated fire quite easily. I wiped a bike command squad with 2 9-man Tac squads the other day, his squad was about 225 points. Gone with one round of fire from guns that were out of range of everything else anyways.