The frame_id you set in rtabmap should be the base frame of the robot, which seems to be base_footprint in your case. Normally, the frame inside the odom topic should be also base_footprint.
Your wheel odometry would be on base_footprint. Is /t265/odom/sample outputting in same frame than your wheel odometry? If so, you may get a TF tree like that:
/map -> /odom_realsense -> /base_footprint -> /realsense_camera