Will Potential Publishers View an MA Dissertation as Plagiarized?
It depends on what you're trying to publish. If you're publishing your MA dissertation as your MA dissertation, then there's no problem. This implies your MA dissertation has never been published before, and the fact that it's available already is unimportant. Preprints are a thing, but publishers happily publish the papers that follow preprints.

However if you are publishing chunks of your MA dissertation as part of some future work - for example, if you took a chapter from your MA dissertation because it works great as an introduction to the next thing you did, and you are trying to publish this next thing - then you are self-plagiarizing. This would be taking something that's already been published and publishing it again, and would not be acceptable.