Jason Todd, The New Red Hood
The first encounter between the heroes and this trio of villains is over before it begins, meaning some viewers might not even notice the third ninja at all (the makers of Young Justice keep this red hooded katana-wielder to the background, since they know exactly when and where to make their bombshell reveal). Once Nightwing, Superboy, and Black Lightning arrive with more back-up, the real fighting begins. Miss Martian freezes Sensei in mid-air, Black Lightning shocks Ubu's weaponry... and Nightwing takes on this mysterious crimson ninja in hand-to-hand combat personally.
The reveal still relies on some comic book knowledge to catch, once Ra's al Ghul arrives to put an end to the fighting, and explain that he can't help them find the missing Markov. Having apparently left behind the evil secret society known as The Light, Ra's is following his own plans, and allows the heroes to depart. As he does, the masked and hooded fighter finally speaks, saying only "Gray...Son." The name of Nightwing isn't impossible for him to know, but the response from Ra's is what seals it: "Ahh, your memories are returning... Excellent."
If you're looking to understand how a highly trained assassin could arrive at the side of Ra's al Ghul, beneath a Red Hood, and slowly recalling his memories of the Batman family, that's as explicit a confirmation of Jason Todd's resurrection as you're going to get.
Red Hood's Story is Only Beginning
Since the story of Jason Todd's resurrection as the villain Red Hood has been changed more than once, fans can be forgiven for missing this connection. Especially when the first return of Jason Todd in Batman: Hush was revealed to be an illusion... later made real, but altering exactly how much of his memory Jason retained (along with how much he aged before returning). So without putting the episode's hint too simply, Ra's is clearly alluding to Jason's resurrection via Lazarus Pit - the same magical bath used by Ra's to maintain his immortality. In the comics, that was exactly how Jason was returned to life after being murdered by the Joker... but like all souls restored by the Pit's magic, he was twisted in the process. His body returned to life, but the person occupying it was a wild, possessed thing. Jason eventually began to rebuild himself under the training of both Ra's and Talia al Ghul.
However, his memories were distorted along with the facts, all as part of a larger plan to fashion him into a weapon against Batman. The two eventually came to blows (and more than a few were exchanged between Jason and Nightwing, the Robin he replaced), but in the end Jason remembered his life, his adoption by Bruce Wayne, and eventually turned the Red Hood into a hero of the Batman family.
Will Young Justice: Outsiders repeat that same story in DC's animated universe, as well? Or is the mask and uniform a sign that this version of Jason's will become a different kind of adversary in a red hood? For that, we'll just have to keep watching.
Young Justice: Outsiders is available to stream now, exclusively on DC Universe.