The bird like monster that 'went on to be gappa' is not true. Bemlar's concept design is seen in the construction of bemlar suit in the gallery. The hero design for Bemlar went on to be used as Hydra.True, both look like they'd become Gappa. But in reality, and if we remember the story of Hydra, Hydra was a hero to the spirit of a young boy who hated cars because he was killed by a car.
Hydra is also one of the only Ultraman monsters to escape and is still alive.
So yeah, it's Hydra on Beyudora and not 2 Bemlars.