I didn't realize that a brushless DC motor is actually AC 3-phase till just now. Thank you for pointing that out. How well does it handle being stalled?
Just found this. L298N + ESC + Brushless Motor. - Using Arduino / General Electronics - Arduino Forum
Found the answer about brushless motors. They should not be stalled, even for a short period of time.
So I'm still on the original question about stalling a PWM controlled DC motor. I may just have to test mine to point of failure. Put it under a fan, run it up to 50%, and hold the shaft stationary. If it doesn't burn out in an hour, I should be good to go.