Yes a morkies tail should be cropped because the maltese and yorkie have docked tails so morkies inherits it
It is the procedure done, however, you don't have to do it.
If it's inherited then it should be long. I don't like to see any dog have their tails cropped or "docked". If their parents have the stubby tail the pups should too. I wouldn't never do it to my dog!
NO dont crop it! they like chasing their tails