One thermostat can control more than one A/C unit, the limit is only the optical visibility of the transmitter (Smarther AC with Netatmo) and receivers (A/C units). You should properly test it in order to verify what is feasible.
Note: if a Smarther AC with Netatmo manages more than one A/C unit through the IR embedded, all A/C units must be the same model of the same manufacturer. They will be all set to the same settings.