Gentoo, at least, is an unspecialized metadistribution that can be used for whatever purpose you can come up with. It can certainly be put on a server, but for someone lacking Gentoo experience the learning curve might be a little steep, and depending on exactly what software you want, compiling it may take a while on an older machine.

So speaking as a Gentoo user, Debian is a not-unreasonable choice for this use case. It’s certainly stable enough.