I read a great example today in the forums.robot.studio where somebody tested this out with success for GO to PLC. You will still have to scale your floating point to a whole number before sending over profinet. From what I understand as long as the bit values are the maximum + and - values needed and twos compliment is selected in the signal params you will be okay. Although you will still have to do some math as the value will be a int when received in the robot.
I will be testing this out tomorrow as well. I have the forum discussion open on my desk that I am referring to and can post a link tomorrow.
In the ABB Technical Overview for System Parameters there is a section going over analog outputs.