Google is seen to test ads in Assistant Results. It was announced by Google earlier that Assistant would now be available on one billion devices.
There was a search performed on an Android phone which depicted an ad for an Executive MBA program in Italy. No official numbers are available from Google since certain percentage of search queries are seen to be migrated to the Assistant.
There is a less probability that Google will place multiple ads in these results. Google might label this as an experiment and maybe paid search ads in the Assistant might not come for quite some time.