Steve, although not exactly like your vault, i have a similar situation with my house. The service disconnect is in the garage (200a panel) with a 150a feeder to the house 13' away. My ground electrode system is between the two. It is really only one system but one of the rods is under the meter base at the garage and the other (2) are under the LB where the feeder enters the house. They are tied together underground with a bare #2 (in the same 24" trench as the raceway). One might argue I only have one ground electrode system for 2 buildings. I don't see the problem.
