This is what I have tried.
I set the "Item collector" start type to "none".
I added an "event interaction" component to the chest.
I created a Game Event in the event editor, and added 2 actors to it.
Actor 0 is the player.
Actor 1 is the Starting Object.
Added a Mecanim Animation node, and had it play the "use" animation. Set the actor to the player.
Added a Legacy Animation node to the chain. Set the actor to the chest (the starting object). Told it to play the "open" animation.
Added a Start Item Collector node to the chain. Told it the actor was the chest (the starting object).
Result:
Mecanim animation played.
Legacy animation did not play.
Item Collector did not pop up dialog.
Removed the mecanim animation from the chain, and reconnected everything.
Result:
Legacy animation did not play.
Item collector dialog did not pop up.
At this point, I'm under the impression that the "starting object" is somehow not the chest, even though that is the item that has the "event interaction" component on it.