RTAB-Map is focusing on real-time mapping for autonomous applications, for which the scale of the environment should be always known while mapping. This is very difficult with a single camera (without additional sensor telling the scale), there will be always a scale drift. It is however possible to feed RTAB-Map with VIO (visual-inertial odometry) to know the scale with a single camera, though only trajectory will be estimated in real-time, no 3D maps. To get a 3D map online, at least a RGB-D camera, a stereo camera or a lidar is required. RTAB-Map could work on a setup more like their configuration using 6 stereo cameras: https://www.skydio.com/videos/#Gh5pAT1o2V8
skydio has indeed an impressive drone, if they open their SDK to work under ROS, it would be a very interesting platform to develop on from a research point of view!