RichFaces is distributed with three jars:
richfaces-api, richfaces-impl, richfaces-ui
The former Ajax4jsf code presents in all three jar files.
Ajax4jsf code did not have any dependencies from the rest RichFaces component set and DOES not have them now.
So, you can use RichFaces with other component libraries that with the same success as it was before refactoring.
RichFaces (Ajax4jsf) as any other Ajax frameworks, change the DOM tree of the browser. So, it is up to screen reader how smart it to read the DOM and understand the changes.
It sounds like some ajax is better than others from this article and things you can do to support it.
Since ajax4jsf generates the AJAX for you does it take do these things to make it accessible to screen readers?