In my group, we don't ask for RP samples usually, unless we've got two people who want the same position, then we'll ask for a sample from each of them and decide who we think is best suited to that role.
But yes, I do consider peoples' age and mother tongue when looking at roleplay posts. Learning disabilities though aren't the first things to cross my mind; I appreciate that they'll have an impact on how a person writes, it's just not the first thing I think of if there a few obvious spelling mistakes. I don't really know many people with dyslexia, ADHD or other disabilities, so I'd put my not noticing them down to unfamiliarity with them.