Yes it absolutely does. They are part of the world around your character, and that world has to be real.
They have be AT LEAST as real to the reader as they are to the "I" person. Sometimes a bit more depth then is required to keep the reader engaged and believing in your story.
Different characters need different levels of depth. The cashier at the store you visit once in your life does not have the debt of your characters current love interest. But they all have to appear to be real, IMO.