I highly doup that vidcard would be pci-x only. pretty much all server mobos have an agp slot if I remember correctly.
I'm sure that guy was just confused aboot some of the technical jargon they used in the specs for the vidcard, so I say just ignore that n' give it a go. You can always return it if it don't work. I think newegg is 30 days moneyback or something like that. Might wanna check the policy on returns just to be safe.