These are 2 different questions.
Yes a single vCenter instance can manage >= 1000 Hosts and it doesnt matter if these are located in the same room, building, city. So if you have another campus DC there just use a single vCenter to manage both locations.
Now the other part... how to protect vCenter when is comes to be the top asset
- Protect it like other VM to with Replication, Metro Cluster Setups
- or use VCSA HA. vCenter can be deployed in a Active/Passive Setup with 2 Instances and a witness
Regards,
Joerg