Jim,
Let's hope it works.
As long as you just the Y cable's male end into the TIU's serial port, and the MTH #50-1032 cable into one of the female ports and the WIU's serial to USB cable into the other female port, I can pretty much guarantee that it will work.
That's the same Y cable that I purchased from Amazon and use on my layout to connect my 3 WIUs to their respective TIUs.