Yep, that's true. The 'lock getting the mount still needs to do the entire quest chain beforehand, but doesn't have to actually buy the items needed (although getting the lodestone makes life a little easier-- having a backup to keep the ritual going just in case). To be honest, the savings isn't that great, only a couple hundred gold.

AFAIK, once the horse has been subdued other 'locks can be summoned to the instance to get their mount (again assuming that they are at the final part of the quest chain). Blizz may have put an end to this though. Regardless, the dreadsteed encounter is one of the coolest things that I've seen in game yet, and would be happy to help out if anybody needs to run it.