I'm also experiencing strange behavior with open-VM-tools. It shows as unmanaged in Vsphere client and no information displayed about ip adresses and hostname, just like you.
I'm using pfSense 2.0-RC1 (i386) built on Mon Mar 14 11:25:06 EDT 2011 on ESXi 4.1.0,260247, em adapters
But even worse, with open-VM-tools installed, it seems that packets are dropped or lost. MSN messenger keeps disconnecting every 30s or so, downloads stalls after 30s
Once open-VM-tools package deleted and pfSense rebooted, everything's fine...