A syndrome is a set or subset of symptoms that suggest a specific disease, so Yes, your can have RLS at the same time as MS. RLS is not a disease and is not a diagnosis.
And it is very common for MS patients to have the set of symptoms needed to be considered has having RLS.
Upon lying down, uncomfortable leg sensations begin: crawling, tingling, or itching in your legs that only get worse with an overwhelming urge to move. People find that they have to get out of bed to stretch and pace the floor. When you lie down again, the restless sensations in their legs start again.
These symptoms are pretty common with the leg spasticity and paresthesias many MS patients get.