Gipson never tried to hide his Romanist outlook, it was the evangelicals who were gushing over him, unconcerned with any doctrinal problems.
Protestants will always have doctrinal problems with Catholics. I liked the movie anyway.
Mel did indeed reach out to evangelicals. He specifically offered to pre-screen "The Passion" for various evangelical notables, and they pretty much universally commended both Mel and his movie. And it wasn't because they "are desperate to unite again with Rome," but because the death and resurrection of Jesus Christ are central to all Christian teaching. The Catholics don't have a corner on the death and resurrection of Jesus.