I have heard that if you format a card 100% ect2/3, Maemo will complain at startup; what you want to do is create a "token" fat partition as the first partition on the card (any size will do) just to shut Maemo up.
Strange. Maybe nobody has played with this in Diablo? Maybe there are problems when the card has more than one partition? It's even reading the ext3 disk from Maemo's built in file manager. I'll let you know if anything weird happens.