Does this do what you want?
http://support.esri.com/en/knowledgebase/techarticles/detail/27427
Isn't that what the ObjectID attribute does? Or do you want the unique attribute to be within a specified range?
If you are working with some flavor of SDE, you can create a trigger that gets pulled when the delta table gets updated; this trigger updates the field. With incremental numbers it gets a little tricky, but I've seen posts that discuss it.