Please try this:
Open the Map Window and look at the Midi Monitor. First hit the hihat when the pedal is down, then hit the hihat when it's up. Does the Midi Monitor show different midi note values between the two? If it does, you should be able to use the [L]-button in the stroketypes list to assign the closed hi-hat and one of the open hi-hats.
If that doesn't work, you could try using CCHihats instead. Check out pages 36-38 in the Addictive Drums manual:
http://www.xlnaudio.com/downloads/manua ... nglish.pdf
(can also be accessed by clicking the [?]-button in the top right corner of the AD user interface)