water proof tub surround?
You absolutely need to water proof the surround. You can likely use any product (durock, hardie, wonder) that is rated for wet use (not "green" board).

You will still need to fully apply a waterproofing to wet side of the backer. I strongly recommend using a physical membrane like kerdi, but plenty of people swear by paint-on treatments like redgard.

Your finished setup will be something like this:

shower air - tile sealant - tile - thinset - waterproofer - backer - studs