I'll second that. In theory, yes, but only if you've got the other hardware to handle it. You'd need to use it with an ArcadeVGA card, or some other hack that would allow you to run the 640x480 interlaced mode. But assuming you had a system setup that could output 640x480 to a CGA monitor, then Daphne would probably work.
But I haven't tried it myself. Both of my arcade monitors are VGA (can do 640x480 progressive, or 800x600 interlaced). I would be very interested in hearing about anyone actually trying Daphne on a CGA monitor.
-etumor