Certainly we know that body doubles have been used before, and the H copy(ies) in this case would likely need to have been for mostly visual purposes,
Ahaha! So each of those "body doubles" could be convinced that there was a real Adolf that they were learning to imitate, and none of them would understand that the whole thing was fake. I suppose it's possible.
Still, from the Bayesian perspective, most people we meet in everyday life are real, flesh and blood, single individuals. The creation of a fictional entity in the guise of a living, visible human being is less probable statistically, so we need evidence to shift the posterior probability away from the priors.
In this case redundancy is mandated, especially given the massive, dualistic christic/antichristic construction around H.
Couldn't redundancy also be provided by having one of Hitler's underlings step in? Some of the characters under Hitler were quite colorful in their own right. Hermann Goring had been Hitler's designated successor.