Yes, but those devices go from an RS-232 DEVICE TO USB HOST, which is not what is required in this situation—which is USB DEVICE to RS-232 HOST. Also, I'd point out that those devices require a DEVICE DRIVER to be recognized by the computer properly.... something which isn't an option with either the VHF or the GPS.
You're right, of course. And based on the little bit
I read today - even if they were compatible at the Physical and Data Link levels, you'd need something to translate the higher level protocol to the NMEA sentences. There is some interesting information here Peter Bennett's GPS and NMEA Site
although some looks older.