The way to figure that out is by looking at the users Class Of Service (COS)
Using end user credentials you can get the COS object through this call -

http://docwiki.cisco.com/wiki/Cisco_Unity_Connection_Provisioning_Interface_%28CUPI%29_API_--_For_End_Users_--_Basics,_Voice_Name,_Greetings#Class_of_Service


The <AccessSTT> field on the COS object will tell you if transcription is on or off.