You could use anything that provides a 4800 baud NMEA-0183 output to the radio.
Right now my Icom M602 is getting it's 0183 data from the NMEA-0183 output from my new Furuno TZT3 charplotter. But this requires the chart plotter to be on and running for the radio to have GPS. For safety/redundancy I'm not entirely pleased with this.
There are such things as NMEA-2000 to NMEA-0183 bridges. Ones that will take the data off the NMEA-2000 network and bridge it in/out to NMEA-0183 devices. I'm looking to add one from Yacht Devices that will bridge between NMEA-2000 and 0183, and WiFi. But there are less expensive options for bridging, or as you've cited, just using a separate GPS antenna.
-- Bill Kearney
2005 Eastbay 47 FB - Solstice