My iphone game is pure c++, not objective c. Iphone devkit comes with gcc, then any language supported by gcc could be compiled by the iphone sdk and runs on iphone with no problems. There are some changes with opengl and opengl-es, glbegin/glend/glvertex/glnormal... it is not suported on opengl-es, it only supports vertex arrays and vbo. That is faster than use glvertex or glnormal etc... but a lot of software that runs with opengl must to be rewrited for opengl-es.

http://en.wikipedia.org/wiki/OpenGL_ES