makeing a custom distro isn't that hard. I made my wardrive distro out of linux from scratch. That is not anything a newbie should jump into but a lot of small distro's use that to get a base.
Its very easy to make a custom redhat installer. They have a kickstart app that you can add in custom rpms and take out what you don't need and get things custom to a certain enviroment. I use that here at work so when we get a bunch of servers in I just load up my custom RH installer disk and hit install a bunch of times and everything is totally done. I don't have to select which packages and such.
So yes its very possible and pretty easy with some reading of course