The Power PC units won't have many (if any) apps written for them. You can built them up to 10.5 at best. For a while they held their value, I had sold many of our old ones on e-bay, but after 2011, they cost more to ship than they were worth. Only people who will find those useful are people with old copies of Final Cut Studio or Pro Tools. Generally it's a starving artist or musician who will always ask the question: "will it run my (cracked) copy of Pro Tools?"
Regarding use for datacenter access: You can try the PMU reset button on the motherboard, and see if it boots in to BIOS or off of a CD. I don't know how Mac savvy you are, but in my dusty archives I might have a bootable .dmg of 10.4 that you could image onto a [PATA] hard drive using carbon copy cloner.
Vic