This post from the National Federation of the Blind's site may provide you with an idea of the capabilities of screen readers designed to handle LaTeX. The post goes into more detail on how to make STEM accessible to visually challenged students.
However, I think Anonymous Physicist is correct in saying you would only be out of compliance if you failed to provide this accommodation to a student covered under ADA who was directly requesting it from you.
At the College level, ADA only requires that the institution make the services available to students that seek them out. Unlike in primary and secondary education where the school is also required to advocate for the student, advocacy is the responsibility of the college student, and they have to notify the school, submit the necessary documentation, usually with a campus accessibility service, and then seek out the accommodation for themselves. That means that they are supposed to notify the instructor of any accommodations they are entitled to under ADA and work with the instructor and the accessibility office to coordinate those accommodations.
I also think Anonymous Physicist gives you good advice to get in touch with the director of your institution's accessibility office. They may be in a position to set you up with publishing software for assistive technologies. They may even have the resources to take your handwritten answer keys and convert them into LaTeX documents.
You may want to consider switching to LaTeX anyway for the points that Anonymous Physicist brought up, that it could help students that do not qualify for ADA accommodations. Things like Spotlight search in Mac OS X will likely be able to index a LaTeX file.
Another advantage would be that if you are in the habit of distributing prior semester keys as study guides, and you have a semester somewhere in the future where you have a visually challenged student, all of the documents will already be in a format you can provide them without the need to convert them.
