well, you only have to "make it available"
You have to do more than "make it available". Since it is being commercially distributed, and isn't accompanied with the complete corresponding machine-readable source code, they need to satisfy section 3b of the GPLv2:
b) Accompany it with a written offer, valid for at least three years, to give any third party, for a charge no more than your cost of physically performing source distribution, a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Sections 1 and 2 above on a medium customarily used for software interchange;
Can anyone who has a Xoom confirm whether it came with such a written offer?
As others have pointed out, this only applies to any GPL'd components of the software, which includes the Linux kernel but little else.
The fact that they will happily sell equipment to decode the transmissions does NOT negate the fact that the transmissions are obfuscated.
In the US, I would argue that using D-Star on amateur radio is already illegal, under Title 47 part 97(a)(4). Since the codec is proprietary, and documentation on the encoded format is not available, the use of the code is clearly an attempt to obscure the meaning of the communication from anyone that doesn't buy D-Star equipment that contains the proprietary codec.
Most people will listen to your unreasonable demands, if you'll consider their unacceptable offer.