In terms of writing articles, anyone who has something worth saying and can say it reasonably well is probably welcome to contribute to stimhack. The regular writers are usually willing to proof an article. If you have a good idea, ask if it sounds worth it and write an article.
I don't speak for the site, but I'm pretty sure that if you have a good topic and can express your ideas well we will all be reading your article on the front page of Stimhack.
Edit: I can't approve articles but I'm personally willing to proofread and help with formatting. Get in touch if you want help.