I haven't seen anyone use a dolly, and I can think of a few reasons why not.

First, a long time ago, I used a dolly for a .25 sized sport plane that was under powered. I found that take-off was "exciting", since if I hit a bump or pothole, the plane could be tossed up in the air a bit before flying speed was reached. With attached gear, this is no big deal, you just come back down on the wheels. With the dolly, the plane frequently feel off the dolly and I had to go get it and try again. Not what you want in a 90 second window.

Second, most combat planes don't have a rudder or tailwheel, so you'd have to rig something up for stearing otherwise you're basically out of control during the take-off run. Could be unsafe, espeically in a crosswind.

Third, the pilots line at many contests is moved way out on to the runway to get proper setback for the spectators. I've been to contests where there wasn't enough runway left to ROG. Plane were hand-launched or catapulted right over the tall grass.

Fourth, you'd have to work out what to do with your streamer, espeically on days where there is a little dew on the grass. Dragging the streamer on the ground wouldn't be a good idea.