I don't think so, but xmonad is in Entropy, so if you wanted to, you could grab the iso of your liking, boot it, type in `equo install xmonad`, log out, and then log into an xmonad session.
...there's probably more to it than that, but it could be done. Sabayon has a few iso generators, so it wouldn't be hard to "roll your own" if you wanted to do it that way.
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