In order to avoid the "exposed copper" beneath the BL652 chip, does this also apply to via's ?

Answer

We recommend covering the vias with solder mask. The bottom side of the BL652 is already covered with solder mask. That being said, we believe it is more of a safe practice just to prevent any possible shorts between the BL652 and any exposed copper on the host board under the module. It's worth mentioning that the BL652 module underside has no exposed copper except the pads of the module.