Don,
For that to work the devices would need the same data and the same baud. And even then, I'm not sure if the dilution of power resulting in splitting the signal would cause a problem. But, it cannot hurt to try. Another option would be to use a USB hub and two serial cables; we've had some users do this with success (but we learned the hard way this doesn't work well if you're trying to use one for ADSB in and another for NMEA out...best to stick with the same type of cable for both nmea outputs)
-Walter