Yes the Diamond card is basically the same as the rest using a stock cooling design. The only differences between the various AGP Pro's that I know of are below .........
The Gecube and Visiontek cards went with a non-standard PCB design and in doing so didn't include a readable temp diode, so no temp monitoring or fan control for those cards. However they may also be more dependable because they went with a different VRM solution as well which doesn't seem to be as prone to overheating. EIther that, or they're not as popuular so you just don't hear much about them.
The Powercolor, Asus, and HIS ICEQ3 Turbo Pro's use a better tha average cooling solution. Although from what I've read, the ICEQ3 cooler fan will develop an annoying rattle from time to time. Also stay away from the HIS ICEQ3 Rev.1 cards. Had two bad cards myself. They had major issues and HIS released a Rev.2 card (V2) with better quality memory, lowered core clocks and higher memory clocks. The Powercolor card's Accelero X2 cooler seems to be a good one but there is no passive cooling of the VRMs and it depends on the fan to provide adequate cooling. It also exhausts the hot air from the card inside the case toward the CPU area of the motherboard. However, it still provides better cooling of the GPU then any of the other solutions mentioned.
As far as the Sapphire goes, the only thing unique about the Sapphire is the power connectors on the card. It has 2 native molex connections. All the others are PCI-E as far as I know, and a adapter cable is required if you need to use molex.