Is it illegal for someone to claim to be a RDH if they are not?

State dental practice acts vary. For example, in New Hampshire (where I reside), it is illegal to practice dental hygiene without a license. So for the first part of your question, it is best to refer to your state's practice act. In regard to the second question, if you have an inactive license, then you have an inactive license. You are now a registered dental hygienist with an inactive license. You do not lose your license unless it is taken away for a VIOLATION of some law.

Kristine A. Hodsdon RDH, BS
RDH eVillage