Yes you can hack every known Wii. There are differences on what you can do on the Wiis, but all are hackable, and all allow playing backups from usb.
1st gen:
BootMii as boot2 possible, downgraded IOS work
2nd gen
downgraded IOS work
3rd gen
downgraded system menu IOS bricks, downgraded other IOS cause a lot of trouble
4th gen
as 3rd gen + drive needs hardmod to read DVD-Rs(if possible at all), usb still works