Does a creature that is both a vehicle and an artifact need to be crewed before it can be equipped?

Equipping a creature and crewing a Vehicle are two completely separate game actions governed by different rules. Equip is an activated ability (CR 702.6) that attaches an Equipment to a creature you control. Crewing a Vehicle (CR 702.122) is also an activated ability that turns the Vehicle into an artifact creature until end of turn.

An Equipment can only be attached to a creature (CR 301.5b). A Vehicle that has not been crewed is just an artifact — not a creature — so you cannot legally equip it while it is not crewed. However, once the Vehicle has been crewed (or is otherwise made into a creature by any effect), it is a creature and can be equipped normally, with no special prerequisite beyond that.

Importantly, the reverse is also true: you do not need to equip the Vehicle before crewing it. These actions are entirely independent of one another. Equipping does not require the target to have been crewed first, and crewing does not require the Vehicle to already be equipped.

Concrete example: You control Smuggler's Copter (a Vehicle) and a Lightning Greaves. You crew the Copter by tapping a 2-power creature, making it a 3/3 artifact creature. You can now activate Lightning Greaves's Equip ability targeting the Copter. You could not have equipped it before crewing because it was not yet a creature.

In summary: there is no rule requiring a Vehicle to be crewed before being equipped. The only requirement is that the Vehicle is currently a creature at the time the Equip ability resolves (CR 301.5b, CR 702.6a).