Seems to work. Until I sold the machine to a customer that needed Oracle (and Linux), I had a Dell 2550 with dual cpu running on FreeBSD 4.9 and it ran fine, including support for the RAID controller and gigabit Ethernet.
Re: OS X
I'm waiting to see what the G5 Xserve brings to the table. I already have one OS X Server for testing purposes and I'm impressed with it. If the G5 Xserve has ECC RAM (or some other method to account for single-bit memory errors) I'll be very happy. And the Apple fiber-channel Xserve Raid disk array is the bargin of the IT industry at only $11k for 2.5 TB of storage. If they update that to serial ATA drives and keep the price down it'll be even better.