In order to get the race to show in the CK, you need to load it up. When you start up the CK, load your follower .esp, make it active, then load the .esm for the custom race you want to use, along with any other esm's (Apachii, for example) that you want the follower to use. ESM's aren't made active, in case you're wondering, they just get selected for use. When you pull up the menu for your NPC, you will then find the custom race listed in the race menu. At that point you can select it and then use the character tabs to customize the appearance.