xymon and monitoring hosts via port forwarding

I have a couple of smaller sites where our connectivity to them is only via
port forwarding over a small business router.  No VPN tunnel setup.
Basically there are a couple of computers there that we'd like to monitor.


Can xymon receive messages from a host via port forwarding?  And what would
the entry in the hosts file look like for such a setup?  Can you give an IP
address and port for it to communicate back the other way, i.e. pings, etc?