You absolutely can use the big easy for fish. They make a bunk bed basket so you could layer more than one rack. The big easy is pretty awesome. I would lightly rub some oil on the fish, still get the fried flavor without the mess.
I know chicken thighs take about 30 mins hanging, I would imagine you could have fish at an appropriate temp within 20 minutes. I would maybe check a piece or 2 at the 15 - 20 mins mark, and watch for that perfect color.