Thermage - Is a Doctor Required to Supervise Treatment?

Each state has specific laws about who can legally provide certain treatments. In California MD's, NP's RN's and PA's are all eligible to perform most laser procedures and injections. In other states there is more laxity as to who can perform medical procedures.
Thermage is a medical procedure and should be performed by well-trained technically educated medical personnel.
Nonmedical providers can unfortunately be under trained and in some states it is truly buyer beware. You'll have to research your state's medical board requirements to get the correct answer to your question.
Thermage can cause burns and scarring if it's not used correctly. Other than myself, I will only allow my Thermage-trained RN to perform Thermage as I believe patient safety is paramount.
Patients need to understand that they always have the option to request the credentials of a treatment provider. If you have reservations about the ability or training of a certain provider or technician (or aesthetician in your case) cancel the procedure. Don't risk your appearance or safety for the sake of politeness.

Each state has different requirements requiring a physician direct of indirect supervision of Thermage treatment or any light or energy base treatments.  In my state this procedure can be delegated to a state license practitioner, i.e. esthetician. There are many states that allow indirect supervision such as the medical director can be off site.  Never be afraid to ask who will do their procedure and how experience they are and how the were trained.