No, ILS/GDPR replication is just replication of routing information, not users in the directory. If you use UDS, you can only find the users that exist in your local directory. You would need to trunk your IM&Ps, assuming the same domain, or federate between them for that to happen.
You should be able to type the URI of a remote user, and dial it without any issue, that's what you'll get with ILS and GDPR.
HTH
java
if this helps, please rate