Mint 17 is basically the system on which I build the appimage, so it is probably not very representative…
yesterday I had it a go with a Live “Debian Dog” distribution, which has an extremely basic environment, and it was working as well (my GIMP appimage still fails on that system, for example).
Maybe @Morgan_Hardwood can give it a quick try on Gentoo?
EDIT: sorry, I did not realise that Sabayon was based on Gentoo!