We are attempting to connect some ESXi boxes at remote locations to a centralized VC. Some are connected via VPN, and those ones work without a hitch. The other sites are connected via 1:1 NAT, with an IP-restricted pass all firewall rule on both ends. The problem we are encountering is that no matter how high we set the heartbeat interval on the VC server (it's now set at 24 hours), the WAN-connected hosts eventually time out and are disconnected. There are no communication problems between sites, and the hosts remain connected without issue for as long as the heartbeat interval is set. All involved ISPs claim that they are not monkeying with UDP or port 902 or any combination thereof (or any other port/protocol for that matter). Surely we aren't the first or only ones to try this - I've seen some VMware documentation on WAN-connected hosts to VC sites, but I've been unable to find anyone with this specific issue. Any additional info or logs that might be helpful I will gladly provide.
(Newest build of VC, various ESXi versions from 4.1 up to newest build)