I've played with USB to serial converters, and the one I have is unreliable in Linux. I have it driving a Power Braille 80, and if too much information comes over the link too fast, Brltty will temporarily lose communications with the PowerBraille. It will eventually regain it, but this is annoying to say the least! It also usually has to try to start about 3 or 4 times before it gets communication with the Braille display. Even in Windows, I usually have to unload and reload JFW to get it to talk to the Braille display. My Dectalk USB is on the real serial port. So, even if you could somehow convince it to work as a module, I don't think you'd get reliable performance out of it. The model is the USA19H converter made by Keyspan. They are one of the more open manufacturers in terms of Linux support, so heaven only knows how bad it would be if using a converter where the drivers had to be reverse-engineered because the manufacturer wouldn't help.
