HBase does not complain if there is no reverse DNS lookup possible for the master or regionserver nodes.
If the master is unable to verify the identity of a regionserver using the reverse DNS lookup, the node is added twice to the list of available regionservers (Once with the FQDN the node presents itself and another one as the IP address).
When this happens HBase is unusable and metadata is corrupted.
Hadoop also relies on reverse DNS but it complains if it is not possible to honor it unless you explicitly disable the lookup in the configuration. On the other hand HBase does not complain and simply does not work if the reverse lookup is not posible.
It can be fixed by simply adding entries to /etc/hosts file with the regionservers, but this can become unmanageable if the cluster can grow dynamically in a cloud service like Azure.