No. I very very very highly doubt it. Your Derm or GP will likely conduct a blood panel which will provide information on your lipids/cholesterol (i.e to check liver values as accutane is very hepatotoxic). It MAY have information on oestrogen, testosterone, LH, FSH, estradiol etc. but I doubt even that.
They will certainly not be testing for the presence of drugs (except birth control), this is in fact illegal and would require your permission.
So just to reaffirm, I would bet my house that they don't test for weed.
And EVEN if they did (which they won't), it is completely irrelevant to them. Cannabis has no interaction effects with Isotretinoin and the only values it really effects are slight elevations in oestrogen and a slight decrease in testosterone (which wouldn't be noticeable and would be within the normal range).
