This is my take at the FreeBSD 11 network configuration on fail-over IPs. Append the following to /etc/rc.conf. In my example em0 is the network interface (use ifconfig to confirm), 51.22.53.90 is the VMs IP-address and 51.22.64.14 is the ESXi host.

ifconfig_em0="inet 51.22.53.90 netmask 255.255.255.255 broadcast 51.22.53.90" 
static_routes="em0_iface"
routes_em_iface="-net 51.22.64.14 -iface em0" 
defaultrouter="51.22.64.14"

We configure DNS resolving using the OVH DNS server 213.186.33.99 by creating /etc/nslookup.conf with the following contents:

nameserver 213.186.33.99

If you lose connectivity after a while check your dmesg for ARP entries changes mac-address (especially your ESXi host/gateway). If this happens you can create /etc/rc.local with:

arp -s 51.22.64.14 00:07:b4:00:01:02

It might not be the most OS-native way, if you have improvements please let me know.