I would not worry about it. There is no seal at the outer bearing like there is at the inner bearing, although there should be a rubber plug on the metal dust cap.
Don’t know how the “professional” performed the service. But sounds like he may have used the zerk to put in grease as directed by Dexter instructions and filled the hub with grease. That is the way it is designed to work. And is fine as long as the rear seal is not leaking. But if you have drum brakes the only way to know for sure is to pull the drum.