It is not possible to export VM/Host Groups or VM/Host Rules from vCenter and import to a new vCenter
vCenter Server 7
vCenter Server 8
The details of VM/Host Groups and VM/Host Groups are visible within the vCenter and can manually be recorded to allow for recreation within a new VC.
Alternatively a PowerShell Module DRSRule is available which allows for the export to a JSON file of all the required information. This can be imported to same VC from which it was exported but as it relies on the unique VM-ID and Host-ID of the VMs and Hosts within the cluster in which it was exported it is not suitable to import to a new VC.