I posted a request for this on ideas.adobe.com a while back, please vote for it!
Argh! I spoke to someone at adobe, and they said that you could do it. They just wouldn't tell me how. Saying, "check the forums and google".
I'm glad that I only got the try version, and didn't actually purchase it.
Now I just wasted the last two weeks of my life learning this...and I'm not very happy.
Don't give up complete hope, it may be possible, I haven't figured it out yet. It seems to me the new web cam access should have all the stuff to do the basics, since many tools consider cameras and scanners equivalent devices - 'imaging devices'. With new AIR 2.0 native application access, you could also use that route if you are in a hurry. I'm also looking at using scripting to the 'container' html to use existing Active-X scanner utilities like WebTwain.
So easy to convince me to work on it again. Ha.
I'm going to try the scanner with the camera functions tomorrow. Have you tried to invoke an image scan, and receive data yet? (That is 100% all that I need to do, btw)
I wrote a quick app to detect a camera, with only my scanner connected, and the scanner wasn't detected. I "Alert.show()"ed the Camera.names, and an empty string was returned.
I don't think that the camera route is the way to go.
I'm going to keep poking around, but I just found a thread from 2008, saying that someone has accessed TWAIN functionality with Air, Java and Artemis. I don't even know what Artemis is...so it looks like I have some reading to do.