Resident Evil 5, as we know it, just isn't possible on the Wii. But that's as we know it. Nothing stopping it turning up on the Wii in some other form.
Capcom's Masachika Kawata has told gamesTM:
Hypothetically speaking, the Resident Evil 4 engine would work perfectly for replicating the gameplay but we would never be able to recreate the graphical quality. A gun shooting game like Darkside Chronicles makes much more sense for Wii so, in short, Resident Evil 5 Wii Edition isn't likely to happen. Having said that, Cavia has surprised us with the quality of graphics in Darkside Chronicles, so it may actually be possible after all…
So Resident Evil 5, no. Resident Evil 5: African Dirtbike Zombie Guided Experience, maybe.