The tracking and conversion codes can absolutely be added via Adobe DTM. We need the codes to be placed on your page without an iframe for Formisimo to track the events being fired.
You can do this by ensuring the codes are placed as a "Sequential HTML" type - this way the codes are placed without an iframe and your form will start to track if configured correctly.
If the codes are placed as a "Non-Sequential HTML" they will be in an iframe and your form will not start to track.
If you are having problems getting your form tracking you can drop me an email or get in touch through Intercom in app. Happy to help!