There's a port of Stella (2600 emulator) that's supposedly being worked on over at tehskeen, but it hasn't been mentioned in close to a year. So it probably got abandoned.
You can play Activision Anthology on the GBA emu though to play some of the 2600 classics on Wii like Frostbite and Seaquest, et al.
AtaWii just emulates an AtariST computer, not games.