My concern with using an underarm gait belt in ALS, Greeneyes, that is less the case for ortho pts, is that the joints are inherently unstable as ligaments lose their ability to constitute the shoulder joint, and the ribs/torso are less mobile as well. The shoulders are not the most stable of joints anyway, so... we could certainly say that's not an option with the flail arm variant, but I would be cautious with the other subtypes as well.
And yes, I know people are using belts, as well as their own arms/body that way, but with the latter there can be a little more even weight distribution. There, the problem is also that caregivers often injure themselves doing lifts, whether acutely or repetitively over time.
All in all, I recommend using the Hoyer-type [floor] lifts or a ceiling lift sooner rather than later. There is no stress on any joints, caregivers are at much less risk. It's a bridge that no one wants to cross, but the alternatives can be really damaging.