Lightbrite……
In many cases they do include Chabah Mikvaot.
For example: I went to the OU website and used its ‘synagogue locator’ I chose the state of Kansas. There were three results:
An OU member synagogue
The Chabad Mikvah
The Community Mikvah.
You must remember the OU is a member organization and synagogues pay a head tax. If a community has a member synagogue with its own mikvak the OU would be doing that member a disservice by also posting a non-member mikvah that could take revenue away from the member organization.
Slightly over 25 years ago I was President of an OU member dues paying shul in a small community that had 7 orthodox synagogues…..4 were OU members, 1 belonged to Young Israel, 1 to Chabad and one was independent. We, member synagogues would be very upset if the OU database led prospective members to non-member synagogues.
Today, when I look at the synagogue locator for that city, it shows both member and non-member synagogues, but puts a large logo on the member congregations.
That city has both a community mikvah and a Chabad mikvah. The community mikvah is open to all. The Chabad mikvah is attached to a private home and is only open to the Chabad community (and in rare circumstances their guests). The Chabad mikvah is not on the OU list.