Yes, you can set an auto-row with an inline object, e.g a HTML block containing the ad code set to 33% in width, on one row. You may then place articles next to it.
Notice, even though the content in the auto-row is set to 33%, the whole row will act as a "locked container". When you publish an article in the above rows, the publishing flow of articles will skip this row. The only way to add articles in the remaining 66% of that specific row, is to manuall copy-paste into it.