Here in pimd you can see it knows about both the openvpn server interface and the gre0 interface

11:48:41.272 Getting vifs from kernel
11:48:41.272 Installing le0 (192.168.0.4 on subnet 192.168) as vif #0 - rate 0
11:48:41.272 Installing le1 (10.99.1.1 on subnet 10.99.1/24) as vif #1 - rate 0
11:48:41.272 Installing ovpns1 (10.98.1.1 -> 10.98.1.2) as vif #2 - rate=0
11:48:41.272 Installing gre0 (10.97.1.1 -> 10.97.1.2) as vif #3 - rate=0
11:48:41.272 Getting vifs from /var/etc/pimd/pimd.conf

On the remote site - which actually has a more complex pfSense setup but neither the gre0 or the open vpn client interface show up:

11:52:21.953 Getting vifs from kernel
11:52:21.953 Installing vmx0 (192.168.224.128 on subnet 192.168.224/20) as vif #0 - rate 0
11:52:21.953 Ignoring vmx0 (192.168.224.87 on subnet 192.168.224/20) (alias for vif#0?)
11:52:21.953 Installing vmx1 (10.28.1.254 on subnet 10.28/16) as vif #1 - rate 0
11:52:21.953 Installing vmx2.27 (10.27.1.254 on subnet 10.27/16) as vif #2 - rate 0
11:52:21.953 Installing vmx2.23 (10.23.3.254 on subnet 10.23.2/23) as vif #3 - rate 0
11:52:21.953 Installing vmx2.24 (10.24.1.254 on subnet 10.24/16) as vif #4 - rate 0
11:52:21.953 Installing vmx2.26 (10.26.1.254 on subnet 10.26/16) as vif #5 - rate 0
11:52:21.953 Installing vmx2.111 (192.168.0.1 on subnet 192.168) as vif #6 - rate 0
11:52:21.953 Installing vmx2.3 (10.18.0.30 on subnet 10.18.0.16/28) as vif #7 - rate 0
11:52:21.953 Installing vmx2.101 (10.42.98.254 on subnet 10.42.98/23) as vif #8 - rate 0
11:52:21.953 Getting vifs from /var/etc/pimd/pimd.conf
11:52:21.953 /var/etc/pimd/pimd.conf:8 - Invalid phyint address 'ovpnc1'
11:52:21.953 /var/etc/pimd/pimd.conf:11 - Invalid phyint address 'gre0'

and the interfaces

ovpnc1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1500
        options=80000<LINKSTATE>
        inet6 fe80::20c:29ff:fe98:1ba6%ovpnc1 prefixlen 64 scopeid 0x12
        inet 10.98.1.2 --> 10.98.1.1 netmask 0xffffffff
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        groups: tun openvpn
        Opened by PID 57519
gre0: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> metric 0 mtu 1476
        options=80000<LINKSTATE>
        tunnel inet 127.0.0.1 --> 10.99.1.1
        inet 10.97.1.2 --> 10.97.1.1 netmask 0xffffff00
        inet6 fe80::20c:29ff:fe98:1ba6%gre0 prefixlen 64 scopeid 0x14
        nd6 options=21<PERFORMNUD,AUTO_LINKLOCAL>
        groups: gre

Is this the rigth group for kernel questions