Datablocks are objects that store all the information about the content in the game. Such as, a gun datablock referencing it's model, projectile datablock, and how it shoots. While the gun projectile datablock declares it's damage, gravity, model, particle datablocks, and so on.
You can spawn 6 guns but it wont use any more datablocks than if you spawned 0. So what I'm trying to say is no, increasing the max physics-vehicles will not use more datablocks. Enabling more add-ons that use content will use up datablocks.