Is there a possibility to check via the Youtube data API whether advertisements can be displayed with a specific video?
I understand contentDetails.licensedContent only shows whether a video was uploaded to and then claimed by that same partner. licensedContent false-videos might still be displayed with ads due to 3rd party rights claims and licensedContent true-videos might just simply not want ads.
You can make use of the ContentOwnerAdvertisingOption API, making use of the GET operation in order to retrieve various information provided by the API. In the result you will see a Boolean type parameter adsOnEmbeds that indicates whether the partner can display ads when videos run in an embedded player.
Hope that answers your question.