I've been testing locking my irradiance cache for a camera-animation only scene so that I can render the full animation without having to do the "irradiance cache prepass" on every frame. It works just like I want it to when I'm doing individual frames for testing but when I change the output settings to render the full image sequence, C4D keeps rendering the prepass for every individual frame.
If you set the mode to camera animation, IR cache, and render to the picture viewer, it should render the whole prepass and then render the frames. Then, if you enable "autoload" in the cache files tab, the next time you render it should not recalculate the cache (unless you've changed something in the scene). If you want to prevent recalculation you can disable the autosave option.