No. That really isn’t what they are for at all. In that case, you would use a socket on the doorknob as your IK target.
IK bones are meant to be animated to match the hands and feet of the model the animator is using to make animations. Because they are linked down to the root, they are not effected by the varying proportions of different models that share the same skeleton. So when you play these animations back, regardless of arm length, the hand IK bones end up where the animator placed them. You can then use them as IK targets for the limbs so that the hands and feet still end up where the animation intended for them to be.
Example: Animation is of character holding something with both hands, directly in front of chest, but the model in game has longer arms than the animation model. Result: The arms cross in front of the chest.
The foot IK bones are also important to doing foot placement.