As long as the two images are relevant and not completely different, so as to confuse the user, it shouldn't be a problem. It is worth noting, however, that the "side" images are no longer used on the Roku 2, as far as I can tell, so it may be a moot point.
the mm_icon_side_hd / sd images are used on the older Roku devices and your channel publication will probably be held up if they don't match the mm_icon_focus_hd / sd images.