Correct. If the motor does have built-in thermal protection though, the nameplate must CLEARLY state that it does. Notice it here, below the second horizontal line:
But "clearly" is subjective... I've seen some that just have the letters "TP" on them, meaning "Thermally Protected", or "TC" meaning "Thermal Cutout".
But if there is nothing on the nameplate of the motor saying that it is internally protected, you must assume it is not and use an external OL relay.
Small 3 phase motors sometimes have TP/TC in them too, it's just not as common as it is in single phase because the 3 phase version has to open all 3 phases.