I don't know what kind of compatibility you are looking for. Dot matrix
printers are not well suited for graphics printing, including host-rendered
custom fonts, so the best course is using one of the the printer's onboard
fonts, which minimizes compatibility issues. I had once used OKI
Microline-182 with printer's embedded font set without problems.
Also linuxprinting.org may be good place to start. (
http://www.openprinting.org/printers?action=search )
According to http://www.openprinting.org/printer/Oki/Oki-ML_320 OKI
Microline-320 seems to work "perfectly" (including graphical printing, I
assume) with a free driver.
