Haven't tried it like that, but it should work fine. I do have an IOpener (as my web-server) hooked up to an 18" LCD monitor using the SVGA out. Of course, it's hanging off of a KVM switch so I can still use the 18" LCD with my main machine.
Other than that, most of the higher-end LCD monitors accept digital input, and you'd need a special card to send the digital signals. Digital is WAYYY clearer -- no more ghosting that you'd see if you use poor-quality VGA cables.
Anyways... Instead of mounting the IOpener motherboard on the back, might I suggest mounting it into the base? That way the motherboard won't get in the way when you want to swivel or rotate that 15" monitor. I figure a medium-sized plastic or aluminum "project box" should fit the IOpener motherboard nicely. Maybe you could even get fancy and make your own back-plate to let power, modem, and USB connections into the Project Box at a right-angle to the motherboard.