HP Up, Carbos, Iron, and etc.: They bring EV's up by how much?
10 EVs. This is not affected by Pokerus or Power Items on the Pokemon.
You may only use vitamins up to 10 times on a single stat. Up to 100 EVs can be provided on an individual stat.
This does make it possible for the player to full EV a Pokemon using only vitamins.
10 / 100 / 100 / 100 / 100 / 100
Total is 510 EVs, the maximum, and can be attained through only vitamins.
Hopefully this answered any thoughts on vitamins