Da IGN:
According to reports from media-crate,ruliweb, and Shonin Jump (magazine) Capcom plans on porting Devil May Cry 3 to GameCube. At first, I had my doubts, but after further reports it appears Capcom will use RE's established 'M' rated stance with the GameCube to sliver in more sales of Devil May Cry 3. Considering the moderately well accepted success of RE on GC, Capcom can use the boost of sales in expectation of DMC3's lower sales due to DMC2's degredation of the 'DMC' name. (Apparently, no matter how good DMC3 is...DMC2's crappiness will just create a more worse atmosphere for DMC3 in the market.)
Furthermore, it was stated that because RE4 has a November release date, and DMC3 has a December release date, they will ship a DMC3 demo with the RE4 game. In IGN's insider message board, IGN's editor Jeremy Dunham has stated that he'll make an official statement