Well anything is possible.. It really depends how different the databases are.
What is important is that that the user ids line up in both databases. Everything from topics, comments, security assignments, etc. is assigned to a user.
You also need to make sure topics and topic assignments are not missing for articles, staticpages, etc
If the dev site has just upgraded plugin tables and the production site just has new records for users and topics (no deletions) then you should be okay but you should really test it and see. If there are say a missing user record then any content that user may have will not be able to display and could have cascading effects elsewhere...
The other spot you would have to update as well would be the geeklog plugins table to make sure all the latest version info, etc is correct for each record.
One of the Geeklog Core Developers.