In older 9 speed systems, MTB rear derailleurs work with STI shifters but fronts do not due to different pull ratio's.

In newer 10 speed systems they may not and with new ratio's coming out in 10 speed road systems, it's very doubtful.

I believe that the new SRAM XX series of MTB 10 speed rear derailleurs will work with the SRAM road brifters.