It's not set in stone, but in an interview with CNET.au, RedOctane
cofounder Charles Huang suggested that the DS
version of Guitar Hero III would include a guitar controller "as long as it makes sense and it plays well." Huang went on to say that RedOctane is "exploring ways to get peripherals on a DS game," and that the company is working on approach with Nintendo's assistance. Given the novel controllers
we've already seen hit the DS, RedOctane's got some work to do to back up Huang's assertion that GHIII on the DS "will play probably unlike any other DS game that has come out," but we're willing to give the company the benefit of the doubt -- they seem to have a handle on that whole "gameplay" thing.
[Via DS Fanboy