CZero said: Can anybody explain the seiyuu joke here? Is Shinku's voice also the Japanese dub voice of Picard or something?
No, Shinku's VA is Sawashiro Miyuki, and of course Picard is dubbed by a guy, Mugihito. Patrick Stewart also portrays Professor X in the X-Men films, and Mugihito also does the Japanese voice in the TV version dub for those movies. Other than that, though, can't think of any connections involving Rozen Maiden, so don't think there's any seiyuu joke there.
I should mention, I checked with the user who originally tagged this "seiyuu_joke". He confirmed that he was just using it for the Picard/Xavier thing, for lack of a better tag.