I know someone that has an amazon which is old and mostly blind, he was in the same enclosure and they did fine, they were best buds. The cockatiels since passed away but had nothing to do with the amazon. It is very risky though and I would recommend it at all.
On another note, my mother had budgies in a cage and hahns macaws in the cage next to them. The budgie ended up getting its head stuck in the bars and during that time one of the hahns macaws decided to rip that poor thing's beak right off. Poor budgie didn't have the top part of his beak meaning it couldn't eat by itself. My mother had to put it out of its misery, she still has nightmares about it.