A Blade is a Rack is a Tower.

The standard normal vSphere  licensing is CPU Sockel based. With vSphere it was one LIC per CPU(up to 32 cores). If the CPU have 34 or Cores you need a 2nd. license.

There are special RoBO packs which license per VM count (max. 25 VMs ) and up to 3 Hosts each 2 CPU per Location. But this is only for customer which have normal licensing with a vCenter Std. already in the HQ.

There is new vSphere+ which starts at 16 cores.

If you have 2 populates Sockets in a Blade you need 2 lics for the standard way. If you have 16 Blades within your Enclosure you need 32 lics.

Its simple math to find out if it make sense to license a dozen of old Server with low core count or just buy new shiny 2x32Core Server and only a few vSphere licenses.

vSphere have SMB Bundles, Accerlatorkits or single CPU for licensing.

Regards,
Joerg