Looking at Batman and Harley Quinn, it certainly looks like a DCAU production. The character models closely resemble The New Batman Adventures. Kevin Conroy and Loren Lester also return as the voices as Batman and Nightwing respectively. The movie also sports many henchmen cameos in one scene. Ubu was one of the first ones I saw.
Despite this, it's placement in the DCAU is quite dubious. Booster Gold is heard talking in the Batmobile signifying this most likely takes place in the expanded Justice League era, possibly before or even a little after the events of Destroyer. This gets muddy though as Booster Gold was never a person of authority nor a spokesman for the League. Not to mention Harley Quinn was rarely seen not along The Joker's side during this time period.
In any event, it was certainly great to see the animated style of Bruce Timm who has said in the past that he would like to go back to his style of art at some point. That could also possibly mean just using DCAU character designs in non-canon stories.
It might still be a while if we find out whether Lex Luthor or Darkseid return after finding the Anti-Life Equation but seeing a direct to video DCAU film interspersed every so often in the DC Universe Animated Original Movies series is a nice start.
Disclaimer: I am using conjecture and speculation. Also, these views are my own and do not represent any authority.