EUO simulates user's actions, like clicking, dragging, casting, etc... It doesn't modify the data stream in any way, just interprets the information and can be scripted to react to those events.
How can they possibly tell the difference between a script drinking a potion and me double clicking the potion? The short answer - they can't. Can they tell the difference of me programming my N52 or my G15 to string together UO macros, and me doing it by hand - No they can't.
Can they scan my computer for EUO? - Nope.
I've been through all this before with the Battlefield series. Punkbuster scanning, etc... had NO effect on scripting at all because there was no way of telling the difference between a script and a user.
What they CAN and are PROBABLY going to do is to calculate the difference in position between where they show a char and where he should be.... maybe put something into the client that sends position and movement info to the server (if it's not already there).
I think this is all about speedhacking and possibly Razor and has little or no impact on EUO use.