I'm not sure about Rotties but GSDs are in the Herding group and are "Shepherds"... so nothing unusual about them herding.
I'm not sure about running all breeds together in coursing. Some breeds aren't...ummm...very dog friendly by nature. The sighthounds have to prove they can run with another dog before entering classes to do so. But I really think you'd be more likely to have issues in some of the non-sighthounds.
There would be a way to make it competitive without running dogs together though, They could score each dogs and place them accordingly. Honestly though, it doesn't matter to me. My dogs love to do coursing but it ultimately is a title for chasing a plastic bag. I'm not going to get all bent out of shape that my dogs can't be more competitive in it, I'm just glad there is now an option for them to do it. I have wished for all-breed lure coursing since I was very first introduced to coursing