Bad, I dont know what you mean by Insulin index, but the digestion is too slow for post workout and will actually slow the absorbtion of the protien as well. There will be no insulin spike.
You should instead take in 40-60 grams of Hi gi liquid carbs. Dextrose is the best, but i heard that grapejuice is also good.
It's a bad idea, for milk is usually the culprit that causes indigestion and bloating problems. Thus, post-workout, your best bet would be something like whey protein (www.proteinfactory.com) and dextrose (www.proteinfactory.com)
Remember, bloating and indigestion can cause absorption problems and prevent proper recovery.
Milk alone shouldn't spike insulin much because of the casein's slow digestion, even though milk does contain some sugar. Probably not the best choice post workout.