Are backup files compatible between 3.x and 2.4.1?

I have an iPod Touch 3rd gen which won’t run iOS 8. I also have an iPad which will. If I upgrade the iPad can the two devices continue to share a backup?

Backups are only guaranteed to be forward compatible. Each new version automatically migrates the configuration to the latest format, so you generally don’t want to share a backup repository like that depending on how old it is.

Thank you.