When hacking is used in context of Gameboy games then I'd normally first think of using external tools such as a gameshark to directly edit memory, rather than game glitches. I'm not sure most people would say missingno glitch is hacking but it is a memory exploit.
Modern fighting games aren't really designed for 6 buttons. I guess if you want to play SF6 with only face buttons that could be neat, but you'd still want to map parry and DI to shoulder buttons. The reality is that developers know that most pad players have 4 face + 4 shoulder buttons and most stick and leverless boxes have 8 buttons.
That said, 6 face button pads definitely exist. Most of the ones I've seen are from Hori, but there are quite a few brands that offer one.