Not that I know of... it has always seemed to me that gnome and kde supported those buttons... I would look at gnome's configuration first... and if nothing there then you could always get down to the nitty gritty.
from when I was playing with setting up the hotkeys it seems that there is a config file or something somewhere on the system that tells linux how to interpret the signals from the keyboard. if the system isn't configured for a specific signal then it just ignores it... but if it is then it tries to handle it as it's told to.
For example... on my laptop I have buttons on the front for playing cds... so I have the usual play, stop, ff, rew, etc. When I'm running enlightenment (this is without config'ing any hotkeys) if I hit the play button on the front of the laptop the system sees that key, is configured to recognize it somehow and the toolbar in enlightenment moves to another position on the screen... I used to be typing and my belt buckle or something would hit the play button on the front of the laptop and enlightenment would start moving itself around... let me tell you... confused the hell out of me for the longest time until I realized I was hitting that button and the system knew about it. In addition the volume up/down buttons send a signal that shows up (in bash) as a ^V or ctrl+V signal... but the system doesn't try to do anything with it... cause it doesn't know to. so it echos it the screen and is done with it...
so make a long story short... all the keys send a signal... just need to tell the system what to do with it, whether that is in gnome or some lower level in the system.