Well I'm no expert on music and to say Michael used something first in his music which has never been done before is extremely hard to to justify. However in terms of POP music I believe yes he brought alot of new elements in which existed in some form in other music genres, popularised them and made them mainstream with others then copied "en masse".
Songs like Heart Break Hotel for example with the sound effects was used consistently in his other songs, sound bites from movies and historical recordings were also common giving songs more mood / ambience. (e.g. Thriller, Beat It, Speed Demon, She drives me Wild, Scream, TDCAU, SIM, Morphine, History, 2000 Watts, Threatened). I belive he was not the first to do this, I'm not sure who is or even how easy it would be to trace this evolution.
I guess MJ's real innovation in music was in his expression of it through his perfomance and look, music video, dance, costume, lighting, special effects etc.
I believe he may have alo innovated in some way in the melding of rythm and melody or there place in the music may even have been different but some other members on this board may be better able to say whether this is the case or not.
Certainly technically I know Bruce Swedien did some amazing stuff, I also know that Mike with his producers produced sounds on his records that are not found anywhere else, so in fact yes MJ created sounds I believe that never existed before and have never been recreated or reused since particularly on his Dangerous and History albums .