Shimano road and MTB rear derailleurs can be operated by road or MTB shifters perfectly OK (this is not true for most SRAM stuff). MTB versions are designed for cassettes with larger big cogs (28+) and with a larger difference between small and large cogs. Road and MTB FRONT derailleurs can only be used with a road or MTB front shifter because the required cable pull is different (unless you use a non-indexed front shifter, which should work with either). MTB front derailleurs are designed for a smaller large ring (some models for a 48 tooth, most for 42-44 tooth).