Is it safe to apply Silvadene to a wound from moh's surgery without washing and drying the wound?

At 3 weeks, skin grafts (if healing normally) should be able to handle topical creams and dressings but is still delicate to sheer forces and pressure. If your surgeon recommends Silvadene twice a day without rubbing or wiping the area, I would ask for clarification on how to exactly apply the Silvadene as to not disrupt the surgical site. Silvadene dries easily and can become "caked on" if not removed or kept moist between dressing changes. This may make it harder to continue daily applications if you are not allowed to wipe or rub the scab. I recommend asking for additional instructions. 

As long as you have no allergy to sulfa,I would discuss with your Mohs surgeon as he should advise you on this. I would suggest you should be evaluated by a board certified dermatologist experienced in this procedure to advise you properly and address your concerns.