Can a driver pass on the white line and gain a position in Nascar?

Yes, they can. The only exception is Daytona and Talladega. It's perfectly legal for a Nascar driver to pass on or go below the white line and gain a position at all racing venues, excluding restrictor plate tracks.

At Daytona and Talladega there are double yellow lines, which is considered out of bounds. Drivers who go below the line at these two tracks can be penalized.