ok, so octopus either needs to be cooked for a very short amount of time (just until it's barely cooked through) to keep the muscle tissue tender or for a very long amount of time (2 hrs plus) to break down the connective tissue. The tenderization methods that involve beating it against a rock or whatever are usually for short-cook methods like grilling from raw.
So if you're baking it in a salt crust or pastry crust, that wouldn't be particularly conducive to short-cook methods... it's going to need to be cooked for at least two hours. The main problem I see with cooking octopus using this method is that octopus gives off a TON of liquid when slow cooking, and it would a) dissove enough salt to make it inedibly salty, b) dissolve the salt crust completely leaving you with a salty mess, or c) both. With a pastry crust, you wouldn't have to worry about the octopus being salty, but you would have to worry about the crust becoming a juice-soaked sloppy mess.
Frankly, I'd just give up on the salt crust. You might be able to fashion a crust using salt and egg whites which would stick together, but I really do think it would be inedibly salty.
If you pre-slow-cooked the octopus and made a gravy out of the cooking liquid, you could definitely get in into a pastry crust. That seems like it's more work than what you're looking for though. Good luck!