Documentary work runs from short branded docs of three to five minutes up to feature-length films. The skills overlap with journalism more than they overlap with commercial production. The team needs to be comfortable in someone else's space, work without a crew of ten, and edit a story out of imperfect material.
If you are commissioning a doc, look at the cinematographer's previous interview work first. The image needs to hold for the whole runtime, and a single bad interview shot can break an otherwise great film. Most documentary teams in this directory work as one or two-person crews.