That is incorrect. This article specifically mentions engineers on the Safari team.
Admittedly more tenuous, but other emails mention HR staffers being fired for cause due to contacting employees from another firm in the cartel. This would send a fairly extreme message to other recruiters about where to direct efforts.
In my own experience, I never heard from Google while at Apple. 6 months after moving into finance, three recruiters from Google contacted me independently of each other. Ironically, the only reason I went into finance at the time was because I needed to move to NYC and Google wouldn't speak to me.