Can Vanguard Armor spawn the tokens on an open battlefield?

No, you cannot play the Recruit tokens from Vanguard Armory directly to an open battlefield.

According to RiftJudge FAQ #8577 and FAQ #8845, Recruit tokens must be played to a valid location, which is defined as your Base or a Battlefield you already control. An open battlefield is not a valid location because you do not control it yet, and Vanguard Armory does not grant you special permission to bypass this standard rule.