I was absolutely under the impression that he did. Why, I do not know.
Although, George Vance's books (which I have) are pretty much an extension of Rabbath and Vance's stances are demonstrated standing, so that makes sense.
The sum of my knowledge of Rabbath comes from net research. My teacher hates it. So, I kind of have to try it in secret.

I have been looking for a teacher locally that teaches Rabbath and have even spoken with Vance as part of my search. No luck as of yet.
There are some things I really like about Rabbath and others I have yet to get comfortable with.
I think his hand/fingering approach makes all the sense in the world. But the bent endpin thing is more troublesome for me. I do appreciate the softness in touch that it allows, but having the neck in on my body seems awkward. I'm 6'4" with a 37" sleeve. It just feels like my elbow has no place to go.