Hi,
Involvement with an institution's ethics committee is a separate position than majority of the members main gigs -- whether that be palliative, IM, cardiology, psychologist, or lawyer (there are folks from many backgrounds), the ethics position is typically something "extra" they choose to take on. That might be paid or voluntary. A masters or certificate isn't required, but can help, with landing a position on committee if more people apply than openings available. However, if it is an employed position, typically they will require some sort of relevant credential.