According to documentation [1] looks like Health checks are supported only for IPv4 Load balancers. 

Now the ovn-octavia-provider allow the user to create HM over ipv4 and ipv6, and although the Load_Balancer_Health_Check entry is created after a HM is created, we can not see that the corresponding Service_Monitor entries are populated to SB DB.


stack@ubuntu2004:~/devstack$ sudo ovn-nbctl list Load_Balancer_Health_Check
 _uuid               : b7cecbef-697a-45f8-a5b3-9c2413ff06b7
 external_ids        : {"octavia:healthmonitor"="908e10c3-e855-418d-95c8-4a3c91db0619"}
 options             : {failure_count="3", interval="30", success_count="5", timeout="30"}
 vip                 : "[fdf0:bfd8:1aa7:0:f816:3eff:fe6b:9f52]:22"
stack@ubuntu2004:~/devstack$ sudo ovn-sbctl list Service_Monitor
stack@ubuntu2004:~/devstack$

So as pointed in [2] the feature over ipv6 will be on an incomming patch, so just open this BZ to visibility and tracking. Also related disscusion can be found here [3]

[1] https://www.ovn.org/support/dist-docs/ovn-nb.5.html
[2] https://github.com/ovn-org/ovn/commit/8be01f4a5329ed1d4c920e0b8488bd4a5410ffb9
[3] https://mail.openvswitch.org/pipermail/ovs-dev/2019-November/364332.html