The roms appear to be baked in to the emulator so I'm not totally sure how (or even if) the rom list could be removed or changed completely, but that's not really my area of expertise. The emulation is hit and miss in places, and some games will completely lock up the emulator (the infamous Virtua Fighter vs Taken 2 being one of them) and there's a load of odd tech demos on there too.
A Dreamcast Mega Drive emulator made by Sega Europe and Sega Japan, which has a super-slick front end, a ton of options (50/60hz, the ability to change console regions, controller configurations, VMU support) and a huge list of 175 roms that spans multiple genres.