"Is the automatically created "10.8 Recovery" partition necessary if I already have Time Machine backing up to an external hard drive? How do I get rid of it if it isn't needed?"
You CAN'T BOOT from a Time Machine backup (shouting intentional). If you remove the recovery partition, and have only a Time Machine backup, you'll have no way to boot if the "main" (internal) system becomes corrupted.
If you want a fully-bootable solution that doesn't require the recovery partition, use CarbonCopyCloner to create a bootable clone of the internal drive on an "external" volume. This can be on an external drive, on a partition on an external drive, or even on a "docked drive" in a USB/SATA docking station.
A bootable clone will be worth MUCH MORE to you than either the recovery partition or a Time Machine backup in a "moment of extreme need".