It depends on the item. I was looking at Starcraft II: Legacy of the Void which qualifies for the promotion, but only if you buy it directly from Amazon.com.

However

This item, sold by Amazon.com, is currently reserved exclusively for Prime members.

The game has been out 7 months, but is restricted to Prime members only, yet Overwatch which just came out, is not. Who knows their reasoning for doing things the way they do, but I am tempted to get the free month of Prime just to get this.