There is an expectation that projects dogfood their own software, but I really can't think of a rational reason for a production server not affiliated with the Arch project to be running Arch.
Rolling release is great for technically competent users to install on their workstations, but why would you ever want a rolling release on a production server?
Well, one thing which I know of several projects doing, is having an Arch server as one of the continuous testing servers. This way you can test against bleeding edge gcc/glibc/whatnot and catch bugs or breaking API changes long before they appear in major distros.
