MacBook – Dual FireWire External HDD and second port performance

Yes - I have routinely used up to 4 self powered devices one one FireWire port.

Tom's hardware report that at idle most laptop sized spinning hard drives use less than 1.5W idle and less than 4W at peak - so firewire should start to run out of power between 8 to 10 drives chained together assuming your mac is putting out at least 80% of the design power and they don't all spin up at exactly the same time.

It's the exact same FW800 / 9 pin connector as most recent macs. The unibody frame has the port set a slight bit deeper on the unibody macs than was common on the non-unibody macs.

Here is the diagram from the MacBook Pro 13 inch (Mid 2010) and the only difference in the newer MacBook Pro is the substitution of an identically sized Thunderbolt port instead of the DisplayPort socket.