Is Congreve's use of character names symbolic of their personalities an effective device?

Yes, and one that has stood the test of time. For example, even today, if we call someone a 'Romeo', we are referring to the main character in Shakespeare's Romeo and Juliet. When characters are defined by their names, it is not necessary for the playwright to explain further what he means. The audience is able to grasp the personality quickly, allowing the playwright to save time and keep the action moving along. So, yes, it is an effective device.