For a WAN deployment, you need to set up the Channel IP addresses in the same subnet as the Management/Public IP.
in the install guide, http://www.vmware.com/pdf/vcenter-server-heartbeat-65-installation-windows-2008-virtual-guide.pdf, WAN deployment, page 21, you can find the following:
"In this scenario, the Primary and Secondary server in the vCenter Server Heartbeat Pair will require unique Principal (Public) IP addresses in each subnet and a unique VMware Channel IP address in each subnet for each server ."
Because you have a WAN deployment, the channel packets (with private IPs) are not routed between the two datacenters where your servers are located. Assign each channel NIC one IP from the same subnet as the management
Since you have different subnets, you will also nee to configure static routing between the channel IP as advised on page 9: "When configured for a WAN deployment, configure the VMware Channel to use static routes over switches and routers to maintain continuous communications independent from corporate or public traffic."