I’d say this is more a general typography question than a locale question. So it’s probably the same for every locale – also considering the reason for the no-break space: Prevent a line break between the number and the unit, which doesn’t depend on the locale.
Good point regarding RTL languages. I’d assume that they are not affected as words in the Latin alphabet are written left-to-right in the middle of RTL text, so it could be the same for SI units. But I have no experience or knowledge about that.