Hi,
yes, that can be done, if you have UCCX Premium, utilizing its HTTP capabilities; provided the TTY endpoint is HTTP capable. Either way, there should be a proxy in between that would convert signals coming from the TTY endpoint to HTTP queries, parse the HTML/XML/textish response and convert them back to signals the TTY endpoint understands.
I have a customer with a different approach, we created a video endpoint/kiosk that calls a group of call center agents who can communicate using sign language.
G.