I tried adding the host by FQDN but it wouldn't let me. Would this be the cause? I don't see why I wouldn't be able to talk to the machine using the FQDN but with the IP it's perfectly fine in our current setup.
Quick edit: I logged in via SSH into the hosts and verified that I could ping other items on our domain via the FQDN, including the vCenter server and the DNS servers. I'm able to ping the hosts via IP but not FQDN from the outside. I'm obviously missing something, what could it be?