A page that is written in valid code is well on its way to being accessible, as well (but the two are not interchangeable!).
Google doesn’t just look at inbound links and mostly ignores meta tags (as both have been massively abused by spammers) – in fact, Google actually traverses pages for contents. If the contents is placed in valid HTML, your chances will be somewhat improved. The second step is using SEO (Search Engine Optimization) – the best way to do that is to write valid *and* accessible code. Things like source ordering and correct *use* of HTML are very important.