You're fine. As you correctly muse, the biggest concern is or should be allowing the jack to roll while its lifts as it'll pull its base under the car via the arc of the lifting arm. Follow all the normal safe jacking rules.
The only concern I'd have, and it's minor, is having a car slip off the jack and going sideways while the mechanic is between a fender/ door and the garage's immovable wall. We all recognize the under-crush hazard, but what about the side-crush? Plan an out, and ensure the rear wheels (both) are chocked and e-braked real well. I can't imagine what forces would cause a car to fall sideways, but I mention this for your vigilance.
The only concern I'd have, and it's minor, is having a car slip off the jack and going sideways while the mechanic is between a fender/ door and the garage's immovable wall. We all recognize the under-crush hazard, but what about the side-crush? Plan an out, and ensure the rear wheels (both) are chocked and e-braked real well. I can't imagine what forces would cause a car to fall sideways, but I mention this for your vigilance.