By the way, I sit on an OSMB for an NIH-funded trial. In general, like with their grant review process, they staff these things with mostly academics in the relevant field. NIH people do attend but they obviously aren’t necessarily experts in every subject where they issue grants.
(“OSMB” or “Observational Study Monitoring Board”, is the equivalent to the “Data Safety Monitoring Board” used in drug trials, the difference is OSMBs are for observational studies whereas DSMBs are for interventional studies. )