You are asking extremely vague questions, so they are difficult to answer. What EQ? Do you mean is ANY form of electronic EQ effective at handling frequencies above Schroeder? Well, it depends what you mean by effective. Do you mean "is there any noticeable or measurable improvement after using the EQ?". If so, yes, usually. I am not sure what you mean by "EQ". Do you mean automated electronic EQ such as Audyssey? Or parametric EQ? Or what? Audyssey usually improves the response above Schroeder. Sometimes it struggles. It depends. PEQ - the same answer - it depends on who is using the PEQ device, how skilled they are, what measuring equipment they have, do they know how to use it etc etc. Can you be more specific in what you want to know? Do you have a specific room problem you want to solve? What version of Audyssey are you using?
It depends what you mean by "effective". Sorry to go round in circles but there is no real answer to your question. It's a bit like asking "Is the weather nice in New York City?". Well, it depends...
Audyssey tries to match the response of the speaker/room combination to its defined target curve. There is information on the target curve in the FAQ. How well it achieves that goal depends on the list of things I mentioned in my previous post.