This DHARMA worker kind of looks like a younger version of David Reyes (Hugo's father) and perhaps Hurley can't recognize him as he enumerates the "cursed numbers" either because his face is partially covered by his helmet or because he is just a neverknown relative of his father who died in the purge but only seen by Hugo on family pictures. It's probably not a coincidence if Glenn readjusts his helmet as Hugo supposedly sees him for the first time in 1977. What's more, Hugo is probably too fascinated by the cursed numbers and the building of the Hatch to pay attention to the face of Glenn. We could go as far as to say that Hurley's father 17 years disappearance is connected to this Reyes lookalike. (e.g. Hurley's father started looking for this lookalike some time after he was killed during the purge because he had no more news from him)