Typically,in previous Honda Hybrids,the 12V battery is only used to power the ECU/BCM/ignition,etc,and the engine was actually started from the big 3-phase IMA motor/generator. Unless the IMA battery is dead,in which case it defaults back to the 12V starter.
If the car has been sitting for any length of time,the IMA battery is probably drained also. If you can get the car started,rev the engine a little,and you should notice it charging the big IMA battery on the dash gauge.
Also,I suggest you check out insightcentral.net for more info on the Honda hybrids/IMA system.