What happens if you get to The End on peaceful?

As John pointed out in the comments, you'll need to play on a difficult other than peaceful to collect the ingredients needed for the Eyes of Ender that are used in the creation of an End Portal. Of course, you can always switch to peaceful before going to the End or "hack" in Eyes of Ender, so the question is legitimate.

As one might expect, setting the difficult to peaceful prevents any Endermen from spawning. However, the Ender Dragon is still present and behaves in the same way.

The Ender Dragon actually does appear in the peaceful difficulty. I tested it in Creative mode and Survival mode. You actually don't need to go into a difficulty other than peaceful. You can trade 7-13 emeralds with for 1 Eye of Ender with a Priest Villager. That is the easiest way to go if you are in Survival with no cheats allowed.

If you put your game on peaceful cheats, you can switch from creative to survival, so you could just get a stack of ender eyes, and switch out to survival.

Anyway, I've tried it, and the ender dragon is there, but no enderman.