Yes, I have set updatedb.conf to not prune nfs, cifs, smb, autofs and set prune bind mounts to "no". 
PRUNE_BIND_MOUNTS="no"
# PRUNENAMES=".git .bzr .hg .svn"
PRUNEPATHS="/tmp /var/spool /home/.ecryptfs /var/lib/schroot"
PRUNEFS="rpc_pipefs afs binfmt_misc proc iso9660 ncpfs coda devpts ftpfs devfs mfs shfs sysfs lustre tmpfs usbfs udf fuse.glusterfs fuse.sshfs curlftpfs ecryptfs fuse
I even get the correct output when checking the --debug-pruning output. Furthermore I use --verbose and tee the output to a indexed_paths.txt file and that txt file contains the files on my other drives.
STILL, when I invoke locate my_video.mp4 it doesn't give me any matches under /media/myusername/, just the things on my bootable drive.
I've tried this on two separate ubuntu 16 installations.
What the (insert expletive) is going on?
The only thing I can think of is my LONG updatedb invocation hasn't finished yet and only when it has does the existing locate.db get replaced. I'm not convinced that that is the real reason because I vaguely recall new files from my bootable disk showing up in the search results even though my updatedb job hasn't finished yet.
Other information
The mount entry looks like this:
/dev/sde1 on /media/myusername/myNtfsDrive type fuseblk (rw,nosuid,nodev,relatime,user_id=0,group_id=0,default_permissions,allow_other,blksize=4096,uhelper=udisks2)
I am using the automounter. I hope that's not causing problems.
