Not exactly. The Slots are calculated based on the host's resources with either default values or - in case of reservations - based on them. Depending on the resource configuration of a VM, it could consume 1 or more slots. A VM with e.g. 4 GB memory would use approximately 17 slots, if the memory slot size is 256MB (i.e. 4GB / 256MB = 16 slots, plus some overhead).
André