This is an assumption.

Based on the quality of other Google products, I think it's safer to assume the inverse: Google's mail servers likely know about a domain's MX records and adjust accordingly without account configuration or external intervention.

Maintaining a system as large as the one they do without this feature would seriously suck for the mail admin - it really has nothing to do with the customer at that point. I wouldn't want to work that job if it did because of a) all the angry people it affected and b) the overhead in my job introduced by a bad programmer.