While I suspect that if you call Nikon or Canon Tech support, they will tell you "don't do it", I don't think you'll have a problem, certainly as long as you don't do it all the time.
I have photographed people welding during some of Pete Lerro's "Rosie the Riveter" photo shoots.....me and 14 other guys. Many of us were shooting with "Live View" or the Canon equivalent, because we did not want to be staring at a welding arc through the viewfinder. If anything, using LiveView exposes the sensor to the light continuously, and as far as I know, none of my cameras, or those of the other guys, have suffered any permanent damage. At the time, I was shooting a Nikon D4 and given what that camera cost, I would not have been doing it if I thought it would hurt the sensor.
If you're concerned, put your camera on a tripod, set your exposure, pre-focus the lens on the spot where the action will be and disable autofocus, then shoot with a remote release. That way, you won't risk injury to your eye, and your sensor's only exposure will instantaneous, vs. the continuous exposure mine got shooting with LiveView.
Be safe!
/Kevin Madore