So one of your comments gave me a better understanding of why you're asking - you see the tag line as exclusionary, and you may have a point from a semantics perspective.
Let's compare the description from the tour to other sites:
English Language Learners Stack Exchange is a question and answer site for speakers of other languages learning English.
English Language & Usage Stack Exchange is a question and answer site for linguists, etymologists, and serious English language enthusiasts.
The Workplace Stack Exchange is a question and answer site about the workplace and other career-related topics. It is for members of the workforce to get answers ...
Stack Overflow is a question and answer site for professional and enthusiast programmers.
Law Stack Exchange is a question and answer site for legal professionals, students, and others with experience or interest in law.
It's pretty boilerplate across sites. Almost every SE site ends that description with "It's built and run by you as part of the Stack Exchange network of Q&A sites. With your help, we're working together to build a library of detailed answers to every question about (topic)".
The ELL description could use some additions to describe our "enthusiasts" and our EFL teachers, but I think most folks don't take these descriptions as a complete and final list of who should participate on a site. How would an unemployed job seeker ask questions about interviewing at Workplace.SE (which is on-topic) if the site is only for workforce members?
When I'm thinking about getting involved with an on-line community, the first thing I do is lurk for a little while and watch to see what kinds of things go on, and what the community standards are. If you do that, I think it's obvious what kinds of folks "belong" in our community and it has nothing to do with which language you speak natively.
In my opinion, our target audience is people who want to learn more and help others learn more about practical English. We're really just a big study group :)