I think SWG are fine with an above ground pool. The risk is that splash out will leave salt on the steel frame which will eventually cause corrosion. This will be a slow process, many years in most cases, and can be avoided by ocassionally hosing down the exposed steel with a garden hose. Several SWG are sold specifically for above ground pools.
Here's MY two cents worth....
A pool is a pool is a pool, regardless of if it's above ground or in ground; vinyl liner, fiberglass, or plaster; 1,000 gallons or 100,000 gallons. You still have water to treat.
There IS no difference in the operation of an above ground salt system or in ground system. It's usually marketed to aboveground pools because they've taken alot of bells and whistles out of it. Basically, given you a simple system. The logic is that above ground pools don't normally cost as much or are as big as in ground pools. Therefore you're not likely to spend as much on a salt system.
An abg pool, with 20,000 gallons will need to be treated just the same as an in ground 20,000 gallon pool. Period!
There. I've said it.
Back to watching the rain fall here in SUNNY SOUTH FLORIDA! Now who was doing that rain dance?????