Of course! In my experience, though, in specialized industries you tend to run into the issue that certain organizations/authorities have a very particular idea on how things should be done. Any average editor might get your content reading well but they wouldn't be much help in getting you approval since they have no idea what needs to actually be changed in order to maximize your chances.
Pretty much the same situation as with grant writing or with investment proposals. Proofreading is straight forward enough but I'm of no help in actually increasing the likelihood of success. It's something that really does require someone who knows the environment and I, well, don't. I'm not a smarty pants.
In my case, I started my business after I'd done most of my college courses. I could spot problems in anthropology and history papers that went beyond the basic mechanics, and when somebody handed me his take-home physical anthropology paper, it had a mistake that would have cost the student serious marks if left in. Since it wasn't my place to make changes other than normal spelling/grammar/punctuation fixes, I phoned him. I told him what the issue was I'd spotted and said, "If you want to fix it, tell me what to change. If you don't want to fix it, tell me and I'll leave it alone. Your decision."
So he had me read the problem paragraph to him a few times, he thought it over, and then read me the corrections he wanted to make. He was very glad I'd caught that mistake - and it's one that only another anthropology student would have caught. Some people might consider this cheating... but I knew this student well enough to realize that it was a mistake brought on by fatigue/carelessness, not by lack of understanding of the subject matter.
As for the nursing students... I learned a lot from them over the years, to the point that I was proofreading fourth-year papers and manuscripts, and sometimes ended up with entire classes as my clients (the classes were smaller at RDC than they'd be at a university). I'd get phone calls that started out tenuous, saying, "I've got this really weird paper I need to do..." and I'd say, "It's the one about Rosemary Rizzo Parse, right?"
They'd say yes, and I told them, "I've already done over a dozen of those. They don't scare me anymore." The client was relieved to hear that, relaxed, got on with writing the paper, and I got on with typing it. That particular paper had very stringent formatting requirements, with some weird terminology that had to be used.
So while familiarity with the subject matter really helps, it's also possible to learn on the job.
Except for philosophy. When it came to those papers, I just did the basic mechanics and wouldn't have a clue if they made any other errors. When the students asked my opinion of their papers, I'd say, "I know nothing about this subject, so I'll take your word for it."
I usually tried to avoid giving opinions of their papers, though. One person asked if I would guarantee that she'd get an "A". I told her that if she wrote a paper her
instructor thought merited an "A", that's what she should get. I said that
my guarantee was that I'd do the very best job I possibly could, and while I always hoped my clients would get good grades, I couldn't make that promise.