It isn't supported in ICS, with the HTC keyboard, or any other similar keyboard (I use Swype myself). This is NOT an HTC issue, nor a T-Mobile issue, but an Android thing. Those keyboards send all the text to the app at once (user swipes the screen, keyboard converts to a word, and then sends the whole "word" to the OS, and the lock screen in ICS will not accept that as valid input. I am thinking that it is for security reasons.
The update bug thread has a few posts about this "issue". You will lickely not find a work around, short of using a different lock style (Pattern or Face Unlock).