Yes, Břeclav is in South Moravia. The dance has name. It's called Verbuňk, which can be roughly translated as "recruitment; dance of recruits". So you can guess, where is the old origin of this dance. But you can be sure that, that now they do it already long time just because of girls (and to confuse Štajerci;-)). The event is called Hody ("feast") and it's in autumn. But despite this fact, they are truly dance around máj/májka (Maibaum)!

The dance is part of Unesco culture heritage of Czech Republic, so I found this in English: http://www.unesco.org/culture/ich/index.php?lg=en&pg=00011&RL=00147 and better and longer info in Czech: http://www.nulk.cz/Informace.aspx?sid=138&em=9 (there is also part about function of this dance)

For more info you have to ask someone from this crazy part of Moravia, but I hope that I helped you at least a little bit.