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.
Really unlikely anyone would die from the experimental vaccine itself (at least in terms of the disease it is based on). Vaccine would be made from inactivated and/or weakened stock.
As far as the vaccine "not working" -- that absolutely is possible. 70-80% protection (that percentage of vaccine recipients would not contract live disease) would be seen as a great success.
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.
A major reason why we do not have Ebola vaccines or drugs is that we simply cannot do the phase 3 efficacy testing in humans. Even the phase 1 safety testing has proven problematic. The FDA has an animal rule--but even for that to apply, we'd need more data on how Ebola affects humans.
When Dr. Jenner invented the smallpox vaccine, he had some observational data to back up his self-experiment. He had noted that milkmaids who got cowpox never came down with smallpox. There is no such observational data to support the testing of Ebola Reston as a potential vaccine for Ebola Zaire. The two viruses are found in different areas of the world--Reston is in Asia, Zaire is in Africa. Testing of cross-reactivity cannot be done in monkeys, since they get fatal illness from both strains. Furthermore, even though the only people who have had Reston did not get sick, there is no guarantee that it does not sicken other people.
From a drug development standpoint, Ebola is really difficult.