you can confirm it's being used by enabling
detailed log and checking the target codec of video files. When transcoding to h264 it should say "c:v h264_qsv" instead of "c:v libx264" in the ffmpeg.exe argument list.
I 'think' you will have to install the Intel MediaServerStudioEssentials, as ffmpeg is compiled against the bindings, but the driver implementation is in the Intel suite.