We have set in place some infrastructure in order to give contributers credit for their work. Firstly, if your code is included in the standard tarfile, your contribution will be noted in ATLAS/doc/AtlasCredits.txt. As the author, you retain the copyright, and thus your name is in the contributed code. We have also modified the installation logger to print the author name for user-provided routines (the exception is the Level 1 kernels, which are simply too numerous for logging). We will make a good faith effort to give due credit for work, but in general, we can't guarantee anything.
As an aside, if fame and fortune are your major motivations, you may want to consider contributing to something else anyway. As the founder of the ATLAS project, I'm still waiting for my first interview with CNN, NBC, etc., or indeed, anyone other then my relatives (and all those interviews go like, "You're in computers, can't you get those wordperfect guys to make it easier to use?").