VMware's documentation is notoriously scattered and poorly thought out in my opinion.
I would play this one on the safe side and go with the 12GB requirement. Can you get by? Probably...especially if you have a small VM environment but why bother with a potential headache?
I dont know if it has a built in 'stop' will cause the install to cease if it detects it doesn't have the minimum requirements. Some software does others do not..no idea where vSphere falls.