That’s not exactly a good example. Yeah, Dagona is definitely an exception, since you can’t play him without having a target. But the failing here isn’t that an Opening Gambit isn’t triggering when it should, it’s that an Opening Gambit is resulting in a minion not being playable.
At least with Deceptibot’s case, the rules implications are pretty straightforward. Opening Gambits never trigger for a minion that enters play unless it was cast from the action bar. Since Deceptibot plainly states the minion is played from the deck, it natrually follows that it would not trigger its Opening Gambit effect if it has one.
Also, @whoshim, duelyst’s terminology never stated that a minion must be played from your hand to be considered ‘summoned.’ Every card that references actively putting a minion in play calls it ‘summoning.’ Even cards that put tokens into play, create a random minion, or replay a dead minion.