9500 is the PCI card 9550/9590 is PCI-x. 9500 works out of the box in CentOS 4 as I have used it there. For hotswap, you need a drivecage that also supports hotswap. The 3ware cage does, and comes with all cabling to get drive lights working. They hold 4 drives in 3 drives/half height 5 1/4 space.
I have a spare 9500S-12 that I could part with if someone needs it. Decided on the 9650-12ML soon after we bought the 9500.
Andrew