There is no documented (and thus allowed) API for the UI (including windows, touch input and other events, etc.) except those in Objective C.
But any experienced programmer who isn't sharp enough to pick up the basics of Objective C in a few weeks probably isn't sharp enough to write a decent iPhone app anyway.
I suppose if you really wanted to be demented, you might be able to do it using very complicated plain C. An Objective C compiler could be written to output plain C plus a support runtime (the first Objective C compiler was reportedly implemented this way). So you could write C macros in the form of post-processed Objective C compiler output, and have those C macros call Apple's Objective C runtime/interpreter using introspection, etc. It might be up to 10X the lines of code and 1/10th as readable, and you would need to be an expert in the Objective C language and runtime to pull this off...
So, yes, it's possible. Have Fun!