From configure.ac it appears that powerpc-apple-darwin is or at least was supported. However, as of now, the best we have on MacOS PPC is ghc 7.6.3 (it does not exist on Haskell website, but I have built it in Macports), 7.10.x fails to build, and won’t be fixed (if anything, I would rather fix the latest version, but that is a long-term project).
Has anyone had any success with this, at least on Leopard?