Can you manage servers in different locations connected by, say, a site-to-site VPN with one vCenter server? If you can, is this a recommended or supported configuration?
Can you?
Definitely, as long as your environment qualifies with the other VMware vCenter requirements and the remote location networks are available to the vCenter server, as you mentioned.
Is it recommended / supported?
As always, it depends. If you have a large number of hosts and vms in each location, it would probably not follow best practices (see Linked Mode). If you have a couple hosts and a dozen VMs in the remote site, it may make more sense.
Linked Mode
Another option is to use deploy vCenter Servers for each physical location, and connect them using Linked Mode. This allows you to view all resources and machines from a single 'pane of glass'.
More info: Enhanced Linked Mode - vCenter 6.0
DR Consideration
If you have only a single vCenter in one location, and that location goes offline, you lose vCenter access to both locations. In a DR scenario, you'll probably have plenty to do and adding to that workload is typically ill advised.
Then again, if it's a 3 person branch office with only file and print services, maybe it's worth saving a couple grand on the extra vCenter license.