100%. Fits with the first sentence on page 114 under Wards, with the definition of Rego on page 78, with the Guidelines in general, and in parallel with other RegoForm Guidelines.
With Imagonem, the Form is species. That is the "stuff", the exact equiv of sand, dirt or gravel in Terram, or heat & light in Ignem. Could one use ReIg to create a ward vs. "light", as opposed to "heat"? I don't see why not. And that's certainly not in the Guidelines.
I'd wager that your friend is just a little vague on what Imagonem encompasses, and how it works - which is not at all uncommon (took me long enough to figure it out!). I'm guessing he's thinking that somehow "illusions" are diff from "species" - when in fact they're the same thing.
Not only can they be moved by Rego, they must move in order to be perceived - there are effectively no "stationary" species.
Try explaining it to him with something like this tragic yet somewhat helpful diagram:
(Otoh, if it's his Saga, he could rule "There is no Imagonem, only 9 Forms" - and he'd be right - for his Saga.) 
What effect were you hoping to get? Is this a theoretical question, or is there a specific end in mind? Is there another way to get there?