"I've read that Rotax carbs are not clamped to their rubbers so that they are dislodged by wild engine vibrations, automatically cutting off their fuel. "
Koreelah, Rotax Carbs fit to their boots exactly the same as a jab carb, if it had no clamp it would get thrown off every start
they do get thrown off sometimes, I've had it happen, but that is only because of the very violent shakes they sometimes exhibit with bad starts on a cold unbalanced engine installation with no airbox supporting the intake end of the carb as in Skyrangers etc