Whether or not to hire a professional editor, or to use UCLA's manuscript consulting service, doesn't have a one-size fits all answer. It depends on the writer and the manuscript. It's not necessary to hire a copy editor, for example, if you're confident in your grasp of the basic points of grammar, or have a friend who can catch glaring errors. All writers miss stuff when they copy edit their own work, by the way. Agents will most often pass if the manuscript contains too many grammatical issues, but a slip here and there won't bother them. A good content editor should help a writer fix sentences that contain glaring errors. Copy editors are required before a work is published but not before submitting.
If you're confident that your novel is ready to publish, copy editing aside, and if you're confident that the scenes all click, the characters fully realized with clear objectives and arcs, and that the story pays off, then you won't need a professional content editor. Many novels are written in seclusion, then submitted to agents, represented, and then picked up by publishers. But often the writer needs someone to read the entire novel through, in depth, and to make comments regarding scenes, stories, and characters, before being able to push the manuscript over that final hurdle.
But be aware that hiring a professional editor does not guarantee that the novel will be published. I know a couple of good novels out there that haven't been picked up yet – though thankfully one less because of recent success story from a student. And hiring the wrong one can also be counterproductive. But if the editor sees what you're trying to do, is thorough and insightful, then at the very least the manuscript will be greatly improved, after you've done the hard work of revision. Because in the end, it's always the individual writer who makes it work.