No need to format, as Mac OS X is optimised for all the Macs it can run on and it even includes the drivers for those.
Your 2008 MBP came with Mac OS X 10.5 Leopard and your 2009 iMac probably came with Mac OS X 10.6 Snow Leopard (if it is the late 2009 iMac), thus the SSD running the newer OS will have drivers for the older hardware.