Not sure about the rape but the brassica will not get hit hard by the deer until after it has been hit by frost. The leaves become sweet after they have been frozen one or twice, I think it has something to do with the starches in the plant being broken down into sugars and carbs.
Brassica is planted in the north in the late summer for consumption in the late fall and early winter, at least in my neck of the woods. Once the frost has hit though the deer move in and mow it down.