The internal PRV on a positive displacement pump is intended only to protect the pump itself.
If the pump is the only source of pressure in the system, you may consider relying on the internal PSV for protection of the larger system from over-pressure. But considering that the internal PSV is not a certified relief device that can be removed, inspected and re-set as necessary, chances are that such a decision would not pass a proper HAZOP review. Most vendors/manufacturers of pumps of this type explicitly state that their internal relief device is not to be relied upon for the protection of external systems for this reason.
