I make exercise recommendations for all sorts of conditions, so I personally do not worry about scope of practice but may require a physician to sign off a form on which s/he could indicate restrictions and often ask the client to bring the exercise prescriptions from physical therapy as appropriate. Here is a link to more information http://www.rls.org/Document.Doc?id=2157.
RLS is one of those strange things where exercise in general helps but when and what is often a matter of trial and error. I do not know of any exercise for RLS alone that is contraindicate but the client may have other circumstances such as poor posture which may set limitations.
The person you work with should see a doctor first to figure out what causes their RLS (fibromyalgia has RLS as a side effect).
Once any underlying condition is ruled out, have them move. RLS runs in my family and we do lots of cardio to help offset this condition.