I believe that Legacy players should be able to beta test, while also letting in people that have never played the game before. This way, at least veteran players will have a chance to explain some of the basics to the new players so that they aren't too lost and confused at what to do, despite if the game is on railroads or not.

If you pit new players and veteran players together during a beta, new players will probably feel more comfortable about talking to others and asking questions that wouldn't be present if the veteran players were not around.