The stock roof rack has a 300 lb capacity, so an awning should be fine. I had a roof rack cross bar get run over by my mothers Q5 when I was repainting it and it didn't deform at all (the plastic parts were removed).
My only word of caution is to not deploy the awning in strong winds. I've seen beach umbrellas bend their aluminum posts in strong wind, I can only imagine what it could do to a much larger awning.
The crossbar slides into the roof rack rails with a dove tail like shape, but what provides the clamping is a screw that threads through a metal plate that slides within the roof rack rails. If the cross bar fails it will be the screws that hold the cross bar to the end cap, not cross bar end cap to the roof rack rails.
