In my experience, split humbuckers don't work out too well. They sound okay, but the drop in output makes it impractical to switch between humbucker and single coil during a song.

Whether or not it would sound good, having all 3 on at once would definitely be a unique sound. As long as the pup outputs are well matched, you should get the characteristics of all 3 pup types crossed with all five selector position characteristics.
--Garrett--