That’s correct, all ROS components are now Omnigraph nodes. To find those, you need to open up Action Graph editor by going to Window → Visual Scripting, and find all ROS related nodes under Isaac ROS (or ROS2 if you enabled ROS2 bridge instead of ROS) section in the list of nodes inside the Action graph editor.
There isn’t a direct way to extract or copy a whole graph from one USD to another for now, so you do need to manually add all the ROS components for your use case.