I can't seem to find any hints towards the fact if Pete is Hyperion. I have looked mostly everywhere, it said he is part of the "Biker" But I am not convinced.
Pyro Pete is not part of Hyperion.
Pyro Pete is a "Biker" which is a group of enemies that are found in the DLC of Mr. Torgue's Campaign of Carnage, not to be confused with Bandits who just happen to be riding bikes. Completely different.
The Biker gangs are not associated, paid by or endorsed by Hyperion.