Thought I'd follow up with our findings:
-even with replication, you can have the same imported alias appear on both systems, it's not an issue
-it seems that only a few objects are identified by the system as which host they belong to and even then, only if the alias is the exact same, and even then, not always in the same spot/column.
For example, for partitions and calling search spaces, if the names are the same, you get the server name in brackets in the first (and only) column, Name. For distribution lists, you get the server name in brackets in the second column, Display Name. For users, you get no indication of which server they are on from the listing. You have to click on it to see that you can not edit the user to figure out that it's on a remote server.
All in all, good news that we can have duplicate userIDs for administration.