How do I get the card to use monitor mode?

To create a monitor mode VAP, see: UserDocs/MonitorModeInterface. After that, it won't be necessary to use the command iwconfig ath0 mode monitor.

You can just add another VAP in monitor mode and it will act just like the rawdev used to in past days of madwifi-old - you can send packets to that device, and they will go out like they would on the old rawdevice.