When using auto discovery rules to get hypervisor from virtual center servers, one gets macros like datacenters. So the detected hypervisors can be attached to hostgroups based on datacenters.
It would be great though, that theses detected hypervisors can (also) be assigned to hostgroups based on the virtual center server instance that detected them.
Right now, it is only possible to put the hypervisors a.) in groups based on datacenters or b.) in static groups like "All Hypervisors".
The same applies to deteced virtual machines.