the hotswapping bay is... well, a physical bay, it'll depend on the drive and motherboard for hotswapping capabilities. when you configure your RAID arrays you will select which disks you want to use in that array, and all other disks will be left untouched. I'd suggest looking at your motherboard or system manual for whether hotswapping capabilities are ok with the disk controller in RAID mode.
for the records, I'm not sure if you know this already;
hotswap- drives can be removed and replaced and the system/OS will recognise the new drive without having to power down and restart
hotplug- the physical case has a quick release bay but the system will have to rebooted in order for the OS to recognise the new drive.