I'm not quite sure when it happened, exactly, but both Corona Cruiser and Pass Transit are now available in Google Transit. The Cruiser is available just like any other transit agency, with bus stop icons on the map with detailed information. The functionality in Banning and Beaumont is in that strange limbo where RTA used to be, with only trip planning functionality but no bus stop icons.
UPDATE: Further complicating matters, it appears that only the Pass Transit routes operated by the City of Banning- routes 1, 5, and 6- are available in Google Transit. Pass Transit 2, 3, 4 and the Cabazon Express are operated by the city of Beaumont, and are not apparently available.
This leaves only two agencies in Riverside County without Google Transit trip planning- Sunline (who says that it's "coming soon") and PVVTA in Blythe.