I don't know whether anyone agrees with him, but Apple doesn't agree.
"Always shut down your Mac Pro before opening it to avoid damaging its internal components or the components you want to install. Do not open your Mac Pro or attempt to install items inside it while it is on."
As Linc Davis has said, "live plugging/Unplugging" NOT RECOMMENDED!
The Mac Pro uses drive connectors that will power up the drive in a predicatble fashion if it is plugged/unplugged "live".
But Mac OS X is unprepared for drives to come and go in this fashion, and even if it did no electrical damage, it may wipe out the directory on one or more drives or crash your Mac.Mac Pro (Early 2009), Mac OS X (10.6.8), & Server, PPC, & AppleTalk Printers