Yes, you read it right. Without being activated, Rohan can't get to War, so it will stop moving on the Political Track at the last step before "at War". This will allow the Shadow to capture parts of Rohan without Rohan being able to muster troops. Of course, the Free Peoples player can activate Rohan with a Companion or the Fellowship, but that would require the use of resources that may best be used elsewhere.
"War is much more fun when you're winning!" - General Martok