If Ebola Reston and Ebola Zaire are too far diverged from their common ancestor, vaccinating with Reston might not be any help at all for Zaire. Cross-immunity must be determined experimentally, since it does not always exist.
That is where the ethical problems begin with this sort of research. The only definitive experiments must be done on humans. Some of them will likely die from the experiments.
That is exactly how the smallpox/cowpox vaccination was developed.
IIRC the original patient was a volunteer - the Doctor vaccinated himself and then exposed himself to smallpox.
Something like that could be necessary with Ebola.