Multiple-partition hard drive on Airport Extreme
No, this isn't possible. According to Apple Support:


  Time Machine can’t back up to an external disk connected to an AirPort
  Extreme, or to an iPod, iDisk, or disk formatted for Windows.


However, the same KB also notes that:


  You can use Time Machine with a Time Capsule, and with USB, FireWire,
  and Thunderbolt disks. The backup disk can be directly connected to
  your computer or be on a network. If the backup disk has been divided
  into partitions, you can use one of the partitions.


You just can't have that drive hooked up to the Airport Extreme.