Yes, there are instructions at http://www.google.com/mobile/sync/ for using Google Sync with iPhone/ iPad that points to http://support.google.com/mobile/bin/answer.py?hl=en&topic=14252&answ… – so that you could use CalDAV.
But, when you already have Google Calendar working well with your Gmail account and you have multiple calendars already working, you don’t have to go through all that. All you have to do is this, as described at <http://support.google.com/mobile/bin/answer.py?hl=en&answer=151674>:
By default only your primary calendar will be synced to your device. You can sync additional calendars by visiting the following page from any web browser:
(Google Apps users can go to https://www.google.com/calendar/hosted/your_domain/iphoneselect, replacing ‘your_domain’ with your actual domain name.)
Select the calendars you’d like to sync, and click Save. The selected calendars will display on your device at the time of the next sync.
Much much much easier.