Social norms about hiring freelance assistants 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.
I see no problem with any of that provided that the funding is appropriate. There may be provision in grants for such aid, for example. Research and publication should be about ideas extending knowledge, not about the manual preparation of documents. 

And RAs often do some of that.