Most of your referrers will probably not know the difference, but pointing out to them that you have it could only be to your benefit.
Better would be to go and meet them in their office, bring along a copy of a recent EMG to show how much better your are and let them draw their own conclusions. However, you also have to have the whole process be better for them - easy scheduling, timely reports, e.g. I fax a copy of the report the same day to outside docs, with the original mailed to them same day.
Keep in mind, though, that most PCPs refer about 1 EMG/month, and most just let their office staff handle the referral, so many end up going to a local hospital. You need to work on them to break their referring habits.