I was on accutane for while also (was smoking regularly) I didn't really notice anything. And the people testing my blood never said anything about thc or testing for any other drug, so I'd think your safe...but you never know. I did however not like the affects of accutane. It drys up your face face a lot (for me it did) and your lips get chapped and what not. My opinion: didn't like it, got off it real quick.
good luck with all that