SCSI Hard Drives uses to be the high performance hard drives used in servers, but it is being replaced by SAS (Serial Attached SCSI). No you cannot mix your older SCSI devices with current SAS devices as they are not compatible with each other. You will need to use your SCSI Hard Drives with a SCSI Host Bus Adapter or SCSI RAID controller.
There are two type of SCSI Drives - 68pin and 80pin SCA. The 80-pin hotswap scsi drives are normally used in servers with a hotplug hotswap backplane. If you want to connect an 80pin sca hotswap drive directly to a 68pin cable, you can use the 80pin to 68pin adapter.
Checkout our Hard Drive Caddy Tray category for the different tray caddy to go with your server.