This movie, along with Superman: Doomsday (2007), has nothing to do with previously established DC animated series. Each film exists in its own continuity.
The term "New Frontier" was used by John F. Kennedy in his acceptance speech in the 1960 United States presidential election to the Democratic National Convention at the Los Angeles Memorial Coliseum as the Democratic nominee. Originally just a slogan to inspire America to support him, the phrase developed into a label for his administration's domestic and foreign programs: "We stand at the edge of a New Frontier - the frontier of unfulfilled hopes and dreams. Beyond that frontier are uncharted areas of science and space, unsolved problems of peace and war, unconquered problems of ignorance and prejudice, unanswered questions of poverty and surplus."
Hal Jordan's fellow co-pilot, Ace Morgan, is the leader of a group of adventurers called, "The Challengers of the Unknown", who starred in several incarnations in the comics. The other team members (or "Challs", as they are called) can be seen during the final battle with the Centre. They are wearing the same lavender shirts and white gloves that Ace is wearing.
As a follow-up to this film, Bruce Timm and Lauren Montgomery wanted to make an animated adaptation of "Batgirl: Year One", but the project was shelved and replaced by Batman: El caballero de Ciudad Gótica (2008).