I'm a little late, seeing as it's been over a decade since you've posted this question, but there are no responses yet, I thought it might be of use to you that I respond. USB Loader GX is the go-to for most of the wii modding community, and it is compatible with fat32, ntfs formatted drives, and "supports" wbfs formatted drives, but I wouldn't use them. As for game file types, it supports wbfs game files in the partitions I listed, and ISO game files in ntfs. There are plenty of tutorials on the internet for you to utilize in order to homebrew your wii, so that won't be an issue. All of the information I stated is irrelevant, as I just clicked on your profile and you were well-established in the wii modding community, so I just wasted 10 minutes of my life explaining this. You were last active on June 10, 2013, which makes me think you've lost an interest in this community, but I hope this information is helpful to anyone with this same question.
I just realized that your question wasn't how to run WIA files on your wii but how to run WIA files in USB Loader GX, so most of the information listed above is irrelevant.
All that aside, I hope you have a nice and peaceful life with the people you love, and see ya later.