"Is August a good time to travel on the Alaskan Hwy and then to Prudhoe Bay on AK 11?"
IMNSHO, August is as good a time as any....much later than that and weather will need to be factored in (not a barrier, just additional stuff to consider).
Keep in mind that the Dalton Highway / Haul Road / Alaska 11 stops at Deadhorse. The Arctic Ocean (and the Prudhoe Bay oil facilities) are a bit further away. Understand there are commercial tours that go out to the ocean, but getting into the oil facilities is a bit more of a challenge and typically requires a special pass (not generally available to the public) from the Operator.