War is the Answer:

In the name debate the Scarab and the Locust have been stated as anomalies.  However, they are mining vehicles not military vehicles.  There is probably another name theme for mining vehicles. 

Also the vampire could be the prototype for an entire new cast of vehicles, ones with the same energy sapping qualities. 

And remember, the vampire is not what the Covenant call it, like all their vehicles.  The banshee is named because of the keening sound of the propulsion system.  What would you think if something flew up to a vulture, rammed two fang like spikes into it, drained its power, and flew away?  You would obviously call it a Vampire!

Honestly I would call it NOS-482 (see if anybody gets that one).

However the Covenant vehicles have always stuck with mytholigical or supernatural names. The Vampire certainly fits this criteria.

The Scarab and the Locust were both included in Egyptian writtings for myths and legends so thats where they come from.

Approval of situation A recognized. Commensing the Cromwell Invocation. Ability restrictions lifted for limited use until the enemy has been rendered silent.