Since only the front truck had traction motors, the weight on drivers was under 45 tons and no Fireman was used.
Some railroads may have used a 2-man crew, but I do not personally know of any, and the ones with which I am familiar had a Brakeman.
In case of a need to provide flag protection, that job fell to the Brakeman. If immediate flag protection was required in both directions, the Conductor joined in (reluctantly). The Conductor did not take a chance on getting any dust on his passenger uniform by lining any switches ahead of or behind the doodlebug. That duty again was performed by the Brakeman.
Santa Fe ran quite a few doodlebugs, some with a Porter-Brakeman instead of a Brakeman. (The Porter-Brakeman was an employee from the Car Attendant seniority roster who wore a blue Trainman uniform and handled switches when required. This later resulted in a ruling unfavorable to the railroad by a Labor Board, costing ATSF a large amount of money.)