My mistake, I was thinking a licensed copy of vSphere with vCenter. In your case, the permissions would have to be set on the individual VMs.
Click a VM > Permissions Tab > Add Users
If you wanted to use Active Directory authentication instead of local host accounts, you can go to
Click on Host > Configuration > Authentication Services
And set up a relationship with your domain. You can then apply AD users/groups to VM Permissions.
Cheers