Accutane can cause some pretty awful changes to the lips including dryness, swelling and easier activation of cold sores.  For this reason, adding another possible irritation to the lips isn't a good idea.

The other reason that this may be a bad idea is that if you do have complications of the filler it may be blamed on the accutane rather than the filler or vice versa.  On the whole it is best to avoid fillers and accutane (and most other surgical procedures as well including lasers, peels and elective surgery).