According to their website,
Writing Raw is a a literary sharing website where writers can upload, review and share their writing.Another poster asks,
This sounds fine, especially for a beginner. Get your work seen and read. But what happens if you then want to submit the same piece to a paying publication....Does [this] count as published?That's a great question, Jimmy (or whatever your name is), and one that comes up often, though I'd refer to any selective publication, paying or non-paying. I'd also add variations on that question that often arise. Does posting your work in a forum where writers exchange feedback count as "published?" What about work you post on your personal website.
Generally speaking publications are not going to consider drafts posted in a forum for feedback as having been previously published. This is really no different than distributing photocopies of your work to the writer's group that meets at your library every Tuesday or reading your work in a workshop setting. True, the piece posted online may be available to more readers, but, presumably it isn't finished, and it's not the final draft you are planning to submit. Furthermore, participants don't go to the site to find reading material. They go to exchange feedback. So, no problem there.
Work posted on your website
If you are planning to submit a piece elsewhere for publication, it is a good idea not to post the entire work on your website. You can post excerpts as a means of advertising your style and voice and perhaps enticing a publisher to take a look. You can also, provided you retain the rights, post previously published work on your site. However, an editor might not be pleased to learn that the piece he just published had already been available on your website for a couple of years.
Work posted in non-selective zines
From what I could tell from a visit to Writing Raw* it is not selective. That is, any writer can post his/her work there. It doesn't need to be reviewed and accepted. Readers can provide feedback, but the purpose of this feedback does not appear to be critique. It's more of an opinion. For example, Narrative invites feedback on their Story of the Week, but one would hardly consider it the same as feedback in a workshop or writer's forum.
So, to answer the poster's question, yes, work posted at Writing Raw and other similar sites would be considered to have been previously published and therefore would not meet the guidelines for most publications and competitions. Furthermore, it is not something you can brag about in a cover letter, because it isn't selective. In fact, mentioning it could go against you. So, until you've lost all hope of publishing in a selective venue, this isn't the best type of site to publish your work.
*This is not meant to be a criticism of Writing Raw. From what I can tell the owners of the site have no ulterior motive but to provide a site for writers to post work for others to read, and there is nothing improper or illegitimate about that. I simply refer to it here as an example of a site where writer post their own work with no vetting. This is the only site I mention by name because others I've known from the past (and considered posting on once upon a time) are no longer around.