It’s not the XAVC-L clips that Sony Catalyst Browse can’t see, it’s the Camera Archive created by FCP X. Using your method, I’ve tried pointing to folders containing AVCHD content and Nikon D7000 .mov files. In all cases the error message is the path does not exist. While Camera Archive is merely a container, that container structure is invisible to Catalyst Browse.
This is the path to a Camera Archive containing XAVC-L content:
Media Drive/FCPX_Cam Archives/Cairns-006_2016-06-17/Private/XDRoot/Clip
And the path to a Camera Archive with Nikon D700 content:
Media Drive/FCPX_Cam Archives/1407_RLK-Party/DCIM/105D7000
Here are a couple of screen shots of my Finder window and part of the Catalyst Browse window.


In the first image you can see the Camera Archives, including the Media Drive/FCPX_Cam Archives/1407_RLK-Party/DCIM/105D7000. But in the second images, none of the Camera Archives appear.