Its not the frequencies of the square wave, its their amplitude (or rather its a combination of the two) that might damage a speaker.
However, since the DAC will only be able to produce a certain range of frequencies within a certain amplitude range, and will filter out the rest, digital clipping is absolutely fine (assuming the speakers aren’t poorly made or defective) as its is impossible for the hardware to produce frequencies or amplitudes above a limit.
The issue comes when you are working in an analogue environment and you send more energy to the speakers than they can handle - or when your speakers are defective or of poor quality and therefore unable to withstand the normal frequency range.
In other words…
… is simply wrong.
No - but that isn’t quite a square wave either, try this …
Pulse.ar(200, 0.5);