I don't think this can be done, not in the US anyway. Large scale tests can be done with populations from high incidence areas. And vaccinated test subjects can be "challenged" (given) with inactivated virus to see if they develop antibodies. It would be unconscionable to expose human subjects to live virus deliberately for any reason.
Mostly true. As you say, the volunteers could be challenged with an inactivated ('dead') virus. Bits and pieces of what once was a virus.
But they could also be challenged with a weakened, "attenuated" strain of the real live virus. From
Although they are occasionally run in sick patients, most viral challenge studies are carried out in healthy volunteers. Subjects are given a challenge strain, which is normally an attenuated virus that, in theory, produces a milder set of symptoms than would the original virus. The investigational antiviral vaccine or drug is administered to the subject, either before the viral challenge is made if the test is for prophylaxis, or afterward if the aim is treatment. Depending on the virus being tested, the volunteer may then be quarantined for a sufficient amount of time to prevent cross-infection, or spreading the virus to the general population.
I presume they will do at least one kind of preliminary challenge to a subset of the volunteers. If they don't, and a larger vaccinated test population in a high incidence area experiences highly negative outcomes, there might be legal hell to pay, in that the investigators did not take reasonable effort to access and minimize risk.