Bob,
I see this sort of thing all the time, just for display and convenience purposes. I put a handful of these hangers on the wall in my studio. My luthier had a fit. Check with your local guitar guru to see if there is a long term bad effect to your instruments before you do this.
And be sure to keep the room humidified and at a constant temp, or you certainly will have some very b ad and expensive problems with your instruments.
Just in terms of acoustics, putting the monitors in a non-bisymetrical arragement is not going to help your mixes.
Bill
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"...it's easier than hitting the kids, and almost as much fun..."
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