The answer is a big "maybe". Apple's own pinout doesn't show the game port outputting MIDI signals, but that doesn't mean its true. If you have the card, I would do testing with a multimeter and see if +5V is present on pin 15 of the game port. If so, I wouldn't connect any MIDI device to the machine as that is supposed to be the MIDI-IN pin!
http://support.apple.com/kb/TA31667?viewlocale=en_US
http://support.apple.com/kb/TA31667?viewlocale=en_US