The IP address argument to ipa-replica-prepare states:

IP address of the replica server. If you provide this option, the A and PTR records will be added to the DNS.

This argument appears to be capable of both multiple addresses, and also accepting v6 addresses. The documentation should be updated to reflect that it can be specified multiple times, and that if a v6 address is provided the correct AAAA record will be created. Perhaps a line such as:

"IPv4 or IPv6 address of the replica server. This can be specified multiple times for each interface of the server, or for each IPv4 and IPv6 address of the server. The correct A or AAAA and the PTR records will be added to the DNS if they do not exist already."