Had stitched Dreameater deployed in a game (with nora leech) but it did not get counted for Payback heroic achivement. I was tired so i dont remember the map, but deffo was last or next to last game i played day before yesterday on either daily or single player. I remember playing it early and due to unexpected detect he died fast, but was deffinitely deployed. Counter was same for all 3 remaining achivements so it was easy to see right away.
There is a known bug affecting some of the heroic achievements, where them doesn't trigger. I can confirm you only need to deploy the champion to make it count.