Transmitting too? Oh that's different, because a transducer usually transmits efficiently only near its resonant frequency. Then it works like a bandpass filter. Assuming its resonant frequency is 40kHz, then it would probably filter your squarewave into a sinewave. If it's resonant frequency is not 40kHz ... well ... the results could be poor.
Without knowing any details of your particular transducers, my best suggestion is to try some bench tests and see what happens!