I have used the mount command to mount non-primary drive storage in to my the file system on my primary hard drive. So the path
/remote-mounts/some-directory actually places me on a USB-attached drive when I change in to it.
Will Time Machine traverse in to the mounted directories and back them up or does it stop at mount points? Is it smart enough to tell that these mounts aren't actually on my primary drive?
Edit: Here's my personal exclusion list with a USB drive mounted. As you can see STUFF is excluded automatically and I can't prevent that. It's un-selectable in the list.