I've never seen it upscaled though. Does it get upscaled automatically if the DS9 DVDs are put into a BluRay player?
Yes, and it looks quite the crap.
I've noticed that movies and TV shows mastered from film upscale very well on my blu-ray player, whereas shows transfered to videotape, like Trek, Alien Nation, Due South, and the 1980s Twilight Zone look positively godawful. I'm no video tech guy, but my own theory is that the VHS noise that may not be that visible in standard definition screws up the upscaling process and makes it look ten times worse. Even the home movies I transfered to DVD look really bad on my blu-ray.