I don't know of any printer that is not "SCO Compatible".
If the printer plugs into a standard parallel port (Possibly USB with later versions of SCO; I've never tried it), or if it can be configured as a shared windows printer, or if it can be configured for TCP/IP network printing it is essentially "SCO" compatible. I have a large number of printers that I print to from SCO, including laser, ink jet, and dot matrix.
What are you needing to print (Text? Graphics?). How are you wanting to connect the printer to your SCO box (Direct port? Networked Printer? Windows Shared Printer?)
As for compatibility, it all has to do with the printer language the printer is using (Raw Text? PCL3? PCL5? Postscript?) SCO comes with Raw Text and Postscript filters. You may be able to get other printer languages from any number of sources, or you can program your own filters (Which is not as hard as it sounds if you have some basic C Programming skills).