i have both an installer partition for rBoot and an "insurance" partition, they are both bootable Mac OS X drives and show up in Chameleon. But I prefer my boot loader as clean as possible and hoped you could at the possibility to hide HFS+ drives too.
I'm super sure specifying it in boot.plist doesn't work, not by partition number nor UUID.
(Some kindred minds:
http://www.tonymacx86.com/viewtopic.php?f=119&t=19139)