Rules Question: if the Falcon drops a non-Smugglers unit, does this trigger? Millennium Falcon (72) reads “Action: Return this unit to your hand to put a Character or Droid unit into play from your hand”. I’m thinking that it will not trigger because the unit was “put into play” and did not pay its cost to “play”. But I need clarification.

There is an additional difference beyond just the cost: if you play a card you have played the card while if you just put a card into play you have not played the card. For the specifics: The Investigation - Specifically prohibits playing the card. Other ways of the card entering play (ie Put Into Play) are not affected. Thus if you name "Yoda," then your opponent would not be able to Play Yoda, but could still put Yoda into play via some other means such as the Falcon or Yoda, You Seek Yoda. Mercenary Support w/ Bossk - Bossk's Reaction is specifically to being Played. Thus, if Bossk is put into play in some other way (including via Mercenary Support) you cannot use his Reaction. Counter example: Backstabber has a Reaction to entering play during an engagement. Thus his Reaction does not care how he came to be in play, just that he moved from an out of play location (hand, deck, discard pile) to in play. The obvious way to get the Reaction to trigger is using the Action on Backstabber to play him during an engagement. However, you could also use the Action from Escort Carrier (Action: Focus this unit to put a Fighter unit or a Precision Flying enhancement into play from your hand or discard pile.) to put Backstabber into play from your hand or discard pile, which would not have him enter already participating in the engagement (because that's not what Escort Carrier does) but would still be entering play during an engagement and thus still be able to trigger Backstabber's Reaction.

As Muddervader said, putting a unit into play is different than playing a unit. Since Falcon's action puts units into play, it can't trigger Spirit.