It is safe to use, but you're always going to risk something if you're doing something against Blizzards TOS. DB hasn't been detected, but I am sure they've got a way that may have "shown" that you may be botting. Previously, they've had invisible aggressive mobs which you've tried to attack but unable too, or that it had high hp so you were unable to kill it.
Maybe the Phantom "unattackable" imp is too blame.