Can I add an ESXi host to more than one vCenter server?

I have a situation where I need to add a host to two vCenter servers. The vCenter servers are divided into two different networks and are not in a linked mode i.e. the other vCenter server belongs to a partner company of us and the host is a shared host between us.

The host is already a member of their vCenter server.

I already configured two management IP addresses of the ESXi host and it is accessible from both networks. However, I don't know if it is safe to try to add the host to our vCenter server as well.

The host can only be managed by one vCenter at a time. But you can move hosts to new vCenters in this manner without disrupting the virtual machines.

No, you can't do that. The vCenter management stack assumes exclusive ownership of the ESXi hosts that it manages.

It will warn you when you try to add a host managed by another server, and if you insist and go ahead, the other server will no longer be able to communicate with this host, and will show it as "dead".