Dance mat compatibility? + Let's hope this deal works out

[Angrist]

A year or 2 ago I thought about buying Dance Dance Revolution: Mario Mix for the GameCube, but I couldn't find a cheap enough copy. Just used ones for €80. Now I searched again, the price has dropped to €40, which isn't too bad for a pretty rare game.

Then I found the best deal:

A GameCube I don't want but can sell or maybe even give away
4 controllers (all 1st party)
5 games I don't want but can sell again (MK Double Dash, Super Mario Sunshine, SSBB, Tony Hawk 4, SSX Tricky... own all but the last)
DDR: Mario Mix incl. mat

for €75

So I mailed the guy, I hope he hasn't sold it yet (or realised how cheap that is).

So here's the question about dance mats. Are 3rd party dancing mats compatible with DDR? There's lots of mats for €15, which seem to have the same buttons. Can I buy one of those for 2-player fun?