Islam would get destroyed by Oliveira.
If it stays on the feet Oliveira would knock him out.
If it goes to the ground Islam would get submitted.
whether he has top or bottom position. Islam does not inflict enough damage and is not a good enough offensive grappler to submit Oliveira. He could not even handle Drew Dober, it took him 10 minutes of top control to find a position to submit Dober, all whilst inflicting next to no damage via GNP.
Islam is a good fighter but if he is smart he will let someone else take the risk against Oliveira, someone who could knock him out, since that is the only place he is susceptible to being beat against the crop of top 10 LWs.