Yeah technically that whole "accessibility improves SEO" thing isnt true except in some pretty narrow circumstances, but I have absolutely used it to get more accessibility sneaked into a site when it's not part of the explicit goals of the client. I much prefer clients who consider accessibility as part and parcel of the project though because when we get a remediation project it's almost always because the client got themselves into trouble which is the worst possible scenario to be doing any of this under.