Not a LoadRunner question, as the conversation coming out of the back of the app could be the same as that of a 32 bit application. In some cases DLLs for the 16 bit subsystem are simply thunked to their 32 bit counterparts for communication with the next upline communications component anyway.
I guess the big question is how old is the app. What is the application architecture. Can you tell us more about the client involved. It is likely that the answer to your questions is contained within the age and the architecture of the application in question.