Unless they can demonstrate expertise/success in ALS specifically, I would bring him home, honestly, if you could handle it. He would qualify for in-home PT and OT, and possibly some hours of skilled nursing, under Medicare, with the right doctor's order. Then you could pick up from there on range of motion exercises, etc. to try to return his joints to baseline function. Stamina/energy should build with proper nutrition and rest -- of which there is often more at home, while trying to build his walking and general activity back up.
It is common for a hospitalist to recommend a post-acute facility when someone has lost strength, but the realities of ALS are not generally appreciated by hospitalists because it is not something they encounter that often.
Infectious diseases such as Covid, and the spread of antibiotic-resistant bacteria such as MRSA and worse, is high in rehab facilities. I would also be concerned that it is very easy for a lab tech or transfer aide to pull too hard on a joint, etc. and cause permanent damage, when ALS is not fully appreciated by everyone on staff. Granted, these risks exist in any hospital, but in close quarters, with staff who can moonlight, it can be higher still. That is why Covid ran rampant through nursing homes.
So I guess I would want to see more evidence of likely benefit before considering the proposed transfer.