I just checked it out, downloaded the directory server iso and testing it in an old x86 using the livecd.
It is a customized gentoo system, complete with portage, eix,...
It has it's own "calculate" custom profile,... comes with most everything for that type of server.
A quick look of it, to change it to a "pure" gentoo system would be a matter of changing the profile, unmerge the sys-apps/calculate* apps, "emerge --sysnc && emerge -uDNv world"
They've just done most of the work for you. You will be much better off by doing your own install, you'll learn more about your system and how to keep it running, and you'll have only the software you want installed and the satisfaction of having accomplished it yourself
