Does a nandroid backup contain the hboot?
Generally speaking, no, ClockworkMod (and other custom recoveries) do not backup your bootloader. You can physically look at your backup directory to verify this, but I have never seen a custom recovery that included a bootloader in the backups. What you typically get is:


Boot partition
System partition
Data partition (also /sdcard/.android_secure depending on the recovery/version)
sdext (if you have it)
WiMAX partition (if you have it)


The general rule is to make sure you have the correct HBOOT version before you restore a nandroid backup, and you'd have to flash it separately.