Dear Wessel,
I'd do the following.
give both servers a static non changing IP:
ldapA.yourdomain.tld, e.g. 10.0.0.1 on eth0 ldapB.yourdomain.tld, e.g. 10.0.0.2 on eth0
These two IPs will always be the same. You can access ldapA or ldapB anytime via it's designated name.
For failover, use an alias:
ldap.yourdomain.tld, e.g. 10.0.0.3 on eth0:0 on the active node
Don't tell heartbeat of openldap and everything should be good.
Brgds