Yes, the running braid in the mane is created in the same way as a french braid. While it works well with a long mane, it doesn't seem to work so well with a very long AND very thick mane.
As for the tail, I have been blessed with a thoroughbred that has a very thick and very long tail. If the rinfgs are very sloppy I will tie it up in a mud knot but since he is only a dressage horse, I no longer have to worry about braiding his tail for the hunter shows. I just make a striaght cut along the bottom (bang cut) and let it keep on growing :)