As stated, it depends on what kind of Scorpionfish you are referring to. That's a big family of varied fish, of varied sizes. A Leaf Fish or Dwarf Lion would be fine in a 30. Rhinopias are amazing if you can get a larger tank, and pay $500 or more for one.
As for Anglers, a 30 gallon would do for Antennarius Maculatus (Warty Frogfish) or Histrio Histrio (Sargassum Angler), but you need a much larger tank for most others. Tiny Commerson Anglers or Painted Frogfish can sometimes look very similar to Warty's so you want to get it from a reliable source so you know what you're really getting. Otherwise it will grow up and make that 30 gallon look like a shoe box.
Either way, you're going to have to train whichever one you choose to eat frozen foods or you have a heck of a live food bill to look forward to.