Pixelmon itself, well, if there is a Minecraft Launcher for Mac, and Minecraft Forge is for Mac, then it should work.
Refer to here, this may help: http://www.minecraftforum.net/forums/archive/tutorials/931485-how-to-download-forge-and-mods-mac
This too: https://www.youtube.com/watch?v=X90yeIm2EHo
Also this: http://pixelmonmod.com/wiki/index.php?title=Frequently_asked_questions#Is_there_a_Pixelmon_launcher_for_Mac_OS_X.3F
Model Rater, Pixelmon Tester, Official Forum Supporter, Gym Development Member!
Not the Pokemon we need, but the one we deserve.