I guess the REAL answer is: It depends.
It really depends on what you are going to run on the server and how mission critical it is. Gentoo shouldn't be used on a 99.99% server, i.e needs an uptime of 99.99 or higher.
There is also a lot of commercial systems that are only certified against certain distributions and also against only a specific version within the distribution. Oracle is a very good example of said system. I do however, run Oracle 9.2.0.1 on my Gentoo PC (but that's only because I know what I'm doing when it comes to Oracle, hint hint).
In general, I think Gentoo is not a better or a worse platform to use as a server. A lot of it has to do with the sysadmin, maybe more than which distro to use.
Bottom line:
- Define your needs
- Verify that all software can run/be supported.
- Only run services needed.
- Pay more attention to security issues than to new software releases.
- Implement and TEST your backup strategy. Make sure you have tested restore (You'd be surprised how many enterprise customer who have never tried to restore what they have backed up. THAT can be costly!)
Make sure that it is a s stable as possible. Don't allow users to log in to the server, but use client programs to connect to the seerver programs they need. Since it is a server, nobody should really work on it
Erik