As a singer, I personally wouldn't want to be a part of that, unless it was something REALLY unique.
You can almost consider AIC to have two lead vocalists, especially with the current line-up and that obviously worked extremely well. I've always dug Mushroomhead as well, especially with that Waylon dude in the band.
I couldn't imagine being just the singer guy or just the screamer guy, especially when it's more than possible to do both. I also couldn't tolerate more than 5 people in a band, way too many cooks in the kitchen.
But hey, if they're both doing something interesting and it's not some kind of gimmick, then more power to ya!