Maybe you already solved this, but if not, I came across this site:
http://wiki.labomedia.org/index.php/Pure_Data_vs_Enttec_Pro

It's in french but I think it says that you simply could send messages to a comport object to set dmx values on the usbpro. If I got it right the message should look like this: [126 6 2 0 0 $1 $2 $3 ...etc $511 $512 231(
Where 126 6 2 0 0 is just to tell that sonn comes the dmx values, and $1 $2 $3... represents the dmx values you want to set on channels 1, 2 and 3.
231 at the end is supposed to be some kind of stop sign.

I am not able to test this since I don't own a DMXUSBpro, but if you get it to work please tell, and i will probably buy one for myself.