Hard drive coolers are rarely a must unless you have a pretty much sealed off HD bay. HD coolers and fans are a good idea however as HDs they should increase the life expectancy of your HD. I would reccomend simply putting a fan in front of or behind your HD so that it blows across it. The Raptor does generate more heat than 7200RPM HDs and isnt cheap, so a fan is probably a good idea. Another thing is there isn't really long term research saying how the Raptors last under heat, so it may be good to be safe than sorry.
Brian