They are. Ryan Trinkle (one of the developers behind this) gave a talk about why they are using Haskell (echoing Tim Sweeney's talk, but adding his own perspective) at a meeting of BostonHaskell. Among other things, they've made a custom iPhone cross-compiler port of GHC that is quite impressive (in the waltzing bear sense)

Since their basic approach is applicable to other platforms, it will be interesting to see if GHC ends up with clean, extensible support for mobile cross-compilation in the future.