You still need bottle caps if you're RNGing for Hidden Power.
You don't need that unless you do unrestricted level 100 battles since at 50, 30/31 IV stats are the same. I can see the need now with the upcoming "No Holds Barred" competition (it needs to be in quotes) because the battles will be level 100. 9 times out of 10, online battles are level 50.