Will this shaft protect my house from corruption/hallow spread?

Solution 1:

No

While the gap plus the blocks will prevent direct spreading of corruption/hallow into your house, corruption also grows vines that can potentially breach the gap from the surface. A sure proof method is to extend the wall above ground at least 6-8 tiles. You can build stairs/rope to scale the wall in earlier phases of the game before you can jump/fly over it.

Solution 2:

Im not sure if it will be enough to protect your house. Three blocks are enough in the underground, but you shouldn't forget about the corrupted vines. You should think about increasing the shaft size to more than six blocks or to fill the air with uncorruptable blocks. To be sure that your NPCs doesn't leave your house, I would build your shaft a bit more away from your house. This will also reserve you building place which you maybe want to use later in the game.