You do not need a USB dongle if you use a USB headset (provided it uses a compatible chipset).
Because kindles support USB OTG, it is just a software issue, and it is certainly possible to do "VoiceView enable" any of our kindles with USB OTG, provided that somebody is willing to figure out how to do that, and that they share their solution with us, and that amazon's lawyers do not stomp on a shared solution.