It will support anything that MyVideos supports. If Daemon Tools identifies it as an image file and can mount it, it will play. You may have to add the .img extension in the dialog I posted a screen shot of above though.
Covers are found in C:\ProgramData\Team MediaPortal\MediaPortal\thumbs\MovingPictures
then you would just have to do a backup of your database.
You can use SQLite browser to have a look in your db. In some table (actually movie_info) is a coverfullpath column.
You will however have to do a complete backup of your db as your unique id's (and thus movie info) can change on a new import...
To complete restore a working situation you have to:
backupyour db (movingpictures.db3)
backup your imagefolders (backdrops and covers)
backup any movie
(this is not considering the complete MP install btw, just MovPic)
Normally when your db get's corrupted, it does not do anything with your covers/backdrops (as far as I can tell, they are not related, apart from a file path in the db).
I do not know if any intelligent logic is behind a new instance/copy of an existing db exists... (that's a weird sentence, but I hope it's clear what I mean...)
I don't think it really gets corrupted, I think that mediaportal cannot connect to my share at some point and it clears the database AND the covers folders. When it eventually does connect, it refills itself, but by then it's missing a lot of info. Can't say for sure, but that's my guess. If this is the case I would think the plugin should check if the movie location is accesible before deleting entries. Now I have made a backup/restore script to make it easier to restore my stuff if something goes wrong.