I succeeded in building RTAB-Map into ORBSLAM2 referring to this forum.
Is there a way to check that ORBSLAM2 is working with RTAB-Map?
Which part of ORBSLAM2 is incorporated as RTAB-Map? (Is it only odometry)
Yes, only visual odometry is integrated. You can select the odometry approach by setting Preferences->Odometry->Odometry Strategy to ORB_SLAM2 and set ORB_SLAM2 vocabulary path below, or set parameters Odom/Strategy=5 and OdomORBSLAM2/VocPath.