I am not really sure about this. I saw that gnome-core checks for gnome-print in its configure scripts. But it "disturbs" me that my System maybe behaves differently only because gnome-print was (by bad luck) compiled after gnome-core.
From what I have seen, this is true, so I have added gnome-print as a dependency. I would prefer to have it as an optional dependency though.
gentoo-core compiles if there is no gnome-print. So you could depend on it iff e.g. the CUPS-flag is on. My concern was, that even if this flag was on, gnome-core compiled without gnome-print "support". But I guess it is ok, to do without if CUPS is deactivated.