I've yet to see a shader produced from any editor that didn't rely heavily on varying inputs that simply HAVE to be generated by the application running them. (Be it Tangents, custom..well Whatever. Just goto shadertech and try to run one of their shaders without a slew of C++ code to back it up.)
However much work it is, it's worth it. UnrealEd does it and it's just an amazing productivity boon for the artists.