i found this pdf: http://manuals.info.apple.com/en/logic/Logic_Control_Surfaces_Info.pdf
it seems indeed logic is able to send meter levels as sysEx (non standard) midi messages. since sysEx messages don't have a fixed length (like 3 bytes for a "Note On") it might get a little tricky to get into this. i'd recommend trying the midi monitor that i mentioned. maybe all your info is in the pdf, i didn't really read it.