Hi, Welcome to HCM.
There are no contraindication to supplements while on Accutane
Since you workout, I'd advise to take whey protein powder as supplement along with egg whites for proteins
To combat side effects caused by accutane take calcium plus vitamin D and fish oil supplement. Also apply lot of moisturizer while you are on accutane since the first thing you'll observe is dryness of skin.
Hope I helped. Feel free to ask followup queries in care of doubt.