I have many friends who tour with and have used traditional guitars live and they don't like the sound of guitar amps mic'd and coming through the vocal monitors either. if you watch rig run throughs with steve Stevens and Steve Vai, you'll notice that they have custom made guitar 1x12 or 2 x 12 cabinets next to the vocal monitors in front of them and that's where they hear they guitar. The monitors in front of them are for vocals and other stuff.
On most big stages There's usually an eq inline with each monitor for feed back control and mid craziness. I just go with the faith that it's sounds better front. That and I walk out with my wireless to listen. But sometimes you just deal with the monitor sound or bring your own. :0)
Thanks, Larry. Great Point.