My mistake, here is the updated document:
But it clearly states:
The updates covered in this licensing brief are described in
the context of Windows Vista Upgrade licenses and Software Assurance purchased
under Microsoft Volume Licensing. However, some updates may also apply to licenses
acquired from other channels, such as original equipment manufacturers (OEMs),
and full-package products (FPPs). Please review the license terms that accompany
the products to determine which updates apply to the software you are using.
To answer the question (according to the above documentation assuming it applies), you can use one Vista license on an ESX host and it is good for up to four VMs.
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