Pat,
Yes, others do use the dubbing brush as Leisenring did. Jim would make up bodies like this and store them on cards that had slits cut into them on opposite sides. This way, he could make up bodies ahead of time to be used later. Big Jim used it for all his dubbed wet flies, and was quite a successful wet fly fisherman. He felt that the body construction was very important and that the tying thread should show through the dubbing, somewhat to give the overall effect of the insect.
The affect should look like this:
Another advantage is you can use different colored thread than the tying thread for the dubbing brush. Sure you can do this with a loop IF you tie on different colored thread. You still have to tie this on separately, so you might as well create the entire brush, then tie it on.
The wax that John (WiFlyFisher) is very good stuff for performing this dubbing application.
John,
I'm sure if you spoke with Jim, he'd tell you that dubbing as Leisenring did is not quite the same as dubbing in a dubbing loop. The results are slightly different.
Mark