If I bought this or something like that, could I use it with games created with Gamesalad?
yes, I believe it would work for android games made with GameSalad.
For iOS games made with GameSalad the controller needs to support Apple MFI controller standard.
Disclaimer I do NOT speak for GameSalad
What @BlackCloak said. The only thing is the viewer doesn't yet support the new MFI standards, so you'll need to publish to get that support for now.
Ok thanks !