If you make content accessible for screen readers, you are effectively making content more accessible for search engines as well [0].
high accessibility overlaps heavily with effective white hat SEO. The goal of accessibility is to make web content accessible to as many people as possible, including those who experience that content under technical, physical, or other constraints. It may be useful to think of search engines as users with substantial constraints: they can’t read text in images, can’t interpret JavaScript or applets, and can’t “view” many other kinds of multimedia content. These are the types of problems that accessibility is supposed to solve in the first place.
high accessibility overlaps heavily with effective white hat SEO. The goal of accessibility is to make web content accessible to as many people as possible, including those who experience that content under technical, physical, or other constraints. It may be useful to think of search engines as users with substantial constraints: they can’t read text in images, can’t interpret JavaScript or applets, and can’t “view” many other kinds of multimedia content. These are the types of problems that accessibility is supposed to solve in the first place.
[0] http://alistapart.com/article/accessibilityseo