In most cases hardware incompatibilities are rare, and tend to often be with specific hardware components. Chances are your server would work, even if its not in the certified hardware list - the list simply means that someone tested to make sure everything does work, and probably ship with an installed, configured version of the OS, with all the necessary drivers.
It very likely will not crash.I've seen other reports that it works fine. Haven't seen any mentions of kernel panics or system instability. Ubuntu gets installed on a wide array of hardware and usually works, so this should be a non issue
On the other hand apparently there's sometimes a problem with the built in graphics adaptor and the default settings - especially if you need fglrx. The link recommends installing ssh during the initial install (something you should do anyway) in case this happens. Should the system boot with no video output, it may be necessary to use ssh or a rescue console to fix the drivers.
It may be neccessary to backup
/etc/X11/xorg.conf, and purge, and reboot and reinstall
fglrx-amdcccle, then rebuild a new xorg file with
sudo aticonfig --initial. I'd note this probably wouldn't be an issue with a server setup that dosen't use any X related functions.