Just posted this on the AA forum earlier:
Yes, I have done it numerous times. You need to be careful however if you are not familiar with ORD or you will find yourself outside of security. They seem to have installed revolving doors at most of the exits along the way so make sure you don't go through any of those. I would budget 15-20 minutes if you're not familiar with the route and are walking at a normal pace. I can easily do it in 10 minutes but I know the route and I move pretty quickly.
If you do find yourself outside of security by mistake and the line in T1 is long, ride the train or walk back to T2 and clear security at the checkpoint next to the old HP desks. There is never a line that long. You can show something shiny (e.g. an AA GLD/PLT card etc) at the elite line for an even shorter line.