It depends on what type of biopsy they do. If they do a punch biopsy, it heals very quickly and doesn't leave a scar. If they go deeper and actually cut with a scapel, then it might leave a slight scar. I've had both and have no scar with the punch biopsy, but the deeper biopsy I did a long time ago still has slight scarring.
It's going to be hard for a dermatologist to really treat your condition unless they are able to do a biopsy. Good luck!