Normally, I would say the more the merrier in terms of adding people as SourceForge developers. I'd be happy to see hundreds of people associated with the project. On the other hand, I'd be a little scared with having hundreds of people I've never met have full write access to a project as detailed and delicate as ATLAS. CVS has marvelous rollback abilities, but I'm afraid as of right now anyway, I don't have marvelous CVS abilities, and so I tend to err on the side of timidity.
What all this whining is coming down to is, you have to first show me the money before I'll add you as a developer :). When you first begin hacking ATLAS, the method to use is to submit patches or code to the list, and if your submission is incorporated into ATLAS, we can then get you added as a SourceForge developer.