I really believe just about any USB based sound card device will work on Linux.
That said, you may have to get a USB sound card and a standard mixer separately. You might look at http://www.behringer.com
and even email support to see if their devices will work on what you want to do.
Interesting, you are the second person to mention behringer in terms of using it with the DV-Dongle. I believe (I will have to contact them) that their device assert presentation of a Sound Blaster compatible device to the OS, which would (ostensibly) make it compatible with the DV-Dongle and the Linux Sound card packet modem device drivers.
I also like that it lets you equalize the audio a bit, which would be nice for podcasting and perfecting my audio for DV-Dongle and Linux Sound Blaster packet operations too. The only thing is the bahringer makes no attempt to deal with asserting PTT when it would synthesize the audio (as more expensive ham radio oriented USB sound cards would), but, there are other ways of dealing with that which are quite minor in design (and I have not been on packet in 20 years, so, its not as important to me as having good audio for DV-Dongle operations).