You need Wally to make textures compatible with hammer.
I believe Hammer uses .wad files, HL2.
(You'll understand it once you get wally)
Just search up some tutorials, they are somewhere around this forum.
I just realized what you're asking.
No, it's not much different except that you cannot use any of the player spawns or ladders that you could normally use for source, also, getting Hammer to export a .dif is quite a hassle, I suggest Torque Constructor, easy to use and exports like a charm.