I was unable to get calendar events to sync from phone to google and google apps calendars, though events were syncing fine the other way - from calendard to phone.
I unchecked "PC Sync" as a calendar in the stock calendar app on htc thunderbolt and then everything passed through normally from phone to calendar. Not sure if it was just that a refresh was executed after a change to active calendars or if that PC Sync calendar (not sure what its for - maybe cable syncing to computer??) was capturing the sync requests incorrectly.
In any case, it appears to be working normally now - though i still cant tell what the refresh frequency is or where the setting is.