Is it considered ethical or appropriate for a researcher to hire a freelance contractor to perform or assist in some secondary tasks related to the preparation of a research papers? To make some concrete examples, what about (1) drawing illustrations, (2) transcribing manuscript notes into Latex, (3) preparing numerical simulations, (4) proofreading, and so on?
The field is mathematics. And the assistant would not be a professional researcher, just someone with some scientific background and relevant skills in Latex, Matlab, or whatever appropriate tools.