Palgia,
Please excuse me writing from a position of ignorance, but I think you may be reading between the lines when there is nothing between the lines to read. You say:
The FAA mandated that for certification of small aircraft (23.149), the published Vmc must be for an aircraft out of ground effect. (which might indicate ground effect DOES affect Vmc).
I would suggest that this quote does not imply that ground effect affects Vmc at all. The FARs tell you how to find Vmc, and they tell you to calculate it out of ground effect for no other reason that to do so in ground effect would be dangerous. You can not imply from this that ground effect either does or does not affect Vmc, IMHO.
(As for whether it does affect it or not, and how it might affect it, I don't know enough to argue for or against the other replies, but I'm reading them with interest!)
FFF
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