Can a condenser or electret microphone be used as a speaker if all necessary related components are included in the circuit?
No. While it probably is possible to cause the diaphragm to move with an applied signal, the resulting audio will be severely distorted and almost completely inaudible. You would have better luck with a dynamic microphone, which is essentially the same construction as a speaker. But again, a microphone element is designed for very small movements of the diaphragm, exactly the opposite of what you want in a speaker.