geni

I thought I'd post the solution to this in case anyone else has the same
issue (I hate finding posts with a problem, and no solution).

I was on the right track, but had to contact PSS to get the correct syntax.
To manually create a connection object when the KCC does not automatically
generate one, you use repadmin /add. However, I was having trouble figuring
out the proper syntax for repadmin /add context destination source. Here's
the command that worked for me. (Server and domain names have been altered.)
PARENTDC1 is the domain controller for the parent domain, which was not
pulling replication changes from the CHILD domain - outbound replication from
CHILD.PARENT.PRI was not working. The forest root domain name in this
scenario (no, this is not its real name) is FOREST.ROOT. So the proper
syntax to manually add the connection object and make the NTDS Settings
appear under Sites and Services is this:

repadmin /add cn=configuration,dc=forest,dc=root PARENTDC1
CHILDDC1.CHILD.PARENT.PRI

and then replication was forced using:

repadmin /replicate PARENTDC1 CHILDDC1.CHILD.PARENT.PRI
cn=configuration,dc=forest,dc=root /force /full

This caused the servers, with their NTDS Settings objects, to reappear. I
then re-created the site and site link, re-associated that site with the
proper subnet, and moved one of the servers to the correct site. About 15
minutes after I did that, the site's NTDS Settings object showed the correct
server as the ISTG.