A couple of weeks ago I converted my external WBFS drive to FAT32. It's working great with the Wii, so no problems there. I did have an issue with my usual WBFS utility, WBFS for MacOS X, where it wouldn't read my partition once I converted the drive. I was forced to find a new utility, which is WITGUI. WITGUI allows me to select a folder instead of a partition to manage. This works great for copying, converting, and managing my games.
WITGUI Website: http://desairem.altervista.org/wordpress/witgui/