I have a similar issue on Windows 7 64bit. What I found is that if you (through Explorer) go to the folder to which the drive is mounted to, and then go into a subfolder, and the type something in the search textbox in the upper right corner, you will get a popup asking you whether you want to index this “unindexed” folder. If you click yes, the indexing service will index the folder.
Now I have no idea how to remove this location from the index as it doesn’t show up in the “Indexed locations” window. But the files are indexed, no doubt! EDIT: It seems that after the folder is deleted or unmounted, one can see the paths in “Indexed locations” window as unavailable.
One could tweak the registry and add mountpoints manually: see here
I also find thet my mount point is correctly registered here: