I used to frequent the site often, haven't been around as of late, but I'm just getting into it. I've done a lot of thinking about the foundation, and I had a question: are all of the doctors at the SCP foundation necessarily doctors of hard science or science at all? Given that a lot of the SCP's have mythological, historical, or religious background, I feel that there has to be several doctors whose sole job is to do research and study of religiously influenced SCP's. For the SCP's that pertain to the Abrahamic faith, They'd have to have Christian, Islamic, or Judaic theologians to help give a foundation of what they are working with.
Like Djoric said, it's fairly obvious that some of the doctors in the Foundation deal with the humanities as well. In 1510, for example, one of the doctors serves as a translator from Latin. It's safe to assume he isn't a mathematician.
I generally use Doctor for whenever they have a doctorate (meaning that their area of study would necessarily be something that a place of higher education could give you a course in), and otherwise I use researcher (for the things that aren't really covered by the universities. Things like the occult, spirituality (not that religion crap, the real stuff), chess, and memetics would generally be the latter.