"T" what hose? This nipple is from the same pipe that is on the other side of the motor, for the heater core return. Joining it to the heater core sending hose, you would be bypassing the core and putting hot coolant right back into the block, this would not be good. The stock set up is designed so the coolant that is cooled off from going through the core will go back into the block.
Here is a flow pic: