TSSZ News has posted concept art of the short CG movie Night of the Werehog. It seems one of the deleted scenes was to feature Sonic and Chip playing the Dreamcast!
Two women who worked on Sonic Unleashed, known as Matsubara (level designer) and Yoshino (character designer), posted on Sonic Team's Japanese blog with information on the making of both Sonic Unleashed and Night of the Werehog.
It was revealed that there was a deleted scene in Night of the Werehog that featured Sonic and Chip playing on a Dreamcast. Here's what they said, talking to someone at Sega's VE Animation Studio:
It's a shame the scene didn't make it into the film, but at least we can see Robotnik's Dreamcast in the opening sequence of Sonic Unleashed!
Kinoshita: Sega products were included in our CGI scenes simply because we had fun making them, and we wanted to convey that sense of fun to our viewers.
Matsubara: I understand. I saw a Sega Dreamcast hidden in there…
Kinoshita: I’m glad you noticed!
Yoshino: Matsubara, don’t be a fool. I didn’t see anything!
Matsubara: You had to be quick in order to spot their secret locations!
Kinoshita: There are these images…
Yoshino: Hey, wait a minute! What was that image just then? Go back.
Matsubara: Sonic and Chip are playing a Dreamcast! I’m feeling a rush of emotion!
Yoshino: But there’s no scene like this in Night of the Werehog.
Kinoshita: This was a story concept that had to be left on the cutting room floor. As you can see, it was never finished. We simply did not have time to include it.
Matsubara: What a waste!