Ale, it's probably possible, but it's also probably more trouble than it's worth, and you'd have to build it yourself. If I were doing it, I'd start with an RPM-based PPC Linux distro (probably Yellow Dog Linux, as it seems to be pretty close to RedHat), preferably with the same or a very similar kernel version (Yellow Dog 2.0 uses a 2.2.19 kernel). Take the equivalent binary RPMs from that, add the .noarch.rpms from the SME CD, and you'll have a start. It probably won't work right away, but it'd be a starting point.
Actually, it'd probably be better to use two versions of YDL. Take the kernel and related RPMs from 2.0 (apparently comparable to RH 7.0), and take the others from 2.1 (seems comparable to RH 7.1). You'll probably have to build some yourself, but Mitel includes the source RPMs for those either on the CD or on their FTP site. If all the relevant software builds cleanly for PPC, you'll be pretty much set. Unfortunately, I don't have a mac to play with, so I don't have any way of testing any of this.