Should I separate research into professional and "citizen science" or amateur? This question was prompted by the sign-up of researchgate, which has three sections for new users; Academia, Corporate/Government/NGO, and Citizen Science.

If I am being paid to do research, regardless of my skill level, then I feel this makes me a "professional" in my field. After all, it's my primary source of income and my "profession". I would count myself as an "amateur mathematician", however the term "amateur" implies I'm not being paid for my work. This work is my livelihood, even my skills are far below that of a genuine mathematician. 

However I am also investigating a wider range of topics than my training, and it involves fields where I am unable to make any contributions however I am studying those fields and even writing small literature reviews for in-house/corporate use. 

While I feel it is fair to claim I am a "blockchain researcher", when I am investigating fields for my company which may have applications but I am currently unqualified in, should I count this investigation as a part of my profession or closer to recreational activity? 

While I am being paid for this rather than it being purely recreational, it is still a field which I am not at the frontier of nor deeply knowledgeable of.
Your broader question seems to be whether you are "truly" a professional researcher given that you are paid to do research but consider your research skills to be far below some of your peers. I suspect this is entirely opinion-based: there is no hard-and-fast definition for the term "professional researcher."

The specific question seems to be whether you should identify yourself as academia, corporate/government/NGO, or citizen science. Given that you are requesting access to this website as part of your official corporate portfolio, I would say that corporate/government/NGO seems like the best choice.