There is no requirement in terms of insurance coverage to be an RDA.
However, the dentist’s practice will usually provide blanket insurance covering any professionals working out of their clinic.
Be sure to ask employers in advance what their insurance covers and where you may need additional coverage.
Keep in mind that it might be a good idea to carry extra liability coverage in the event your clinic or place of employment does not have a policy that covers you or that does not adequately cover you while you work.