Hi,
If you see rtabmap's graph (rtabmap_ros/MapGraph) in rviz, yes it is localized.
You can echo the transform between /map and /odom, if not identity, it is localized:
$ rosrun tf tf_echo map odom
On terminal, in the status message sent by rtabmap node you would see "(local map={Not zero}, ...)" when localized.
cheers