I'm pretty sure its just the iCloud email account since you can't sync any other email accounts via iCloud.
I checked here but it wasnt too specific: http://support.apple.com/kb/HT4859.
....or just the iCloud email account?
I believe iTunes backup covers all accounts and I have been assuming that iCloud Backup does the same but I am not sure.
I can't find it in any documentation. If you could paste in a link to documenation, that would be helpful.