As far as I know there is know cert you can get for SEO work. I may however be wrong interested to see what others say. I know a web design class would be good as a properly coded site will do better then a bad coded site.
we have 2 on staff designers so the code is always xhtml/css verfied and very tight so that part is good to go. it is the rest of the package I would be interested in. submitting to the right directories, keywords, etc.
I would like to know it from all angles so I can really nail things down and make seo work for our clients