Aside from Bruce Wayne acting as the mentor to Terry McGinnis, yes.
Barbara Gordon (aka Batgirl) makes plenty of appearances within the series as the current police commissioner of the Beyond era, taking the place her father, Jim Gordon, did years before. Unlike her comic counterpoint, this Barbara Gordon was never shot by the Joker and paralyzed from the waist down. The series does make a veiled reference to that storyline: the first time Barbara Gordon appears in the Bat Cave, she looks at her old costume (set in a display case beside the vintage Batman, Robin and Nightwing suits) and says to Bruce, "I see you sewed up the bullet holes." Presumably, she gave up her Batgirl identity due to slowing reflexes due to age or perhaps, like Dick Grayson (the first Robin/Nightwing), simply got tired of Bruce's endless obsession with the criminal element and went her own way.
Alfred Pennyworth gains a mention at least twice.
There is a street gang called 'The Jokerz' who model themselves upon the original Batman's nemesis, however they are considered to be little more than nuisances by comparison to the psychotic murderer the original Joker was.
The original Joker himself is able to return for the feature film 'Return Of The Joker', despite having been dead for many years. In this feature, two twin Jokerz named Dee-Dee are strongly hinted to be the granddaughters of an elderly Harley Quinn, who had moved on from a life of crime. Also in the movie, Tim Drake, the second Robin from the Animated Series (and third from the comics) plays a major role. Dick Grayson, the first Robin who went on to become Nightwing, also gets a mention in the movie as well as once in the series (both times by Barbara Gordon). It is indicated that he is still alive and well in the Beyond timeline though he never makes an appearance.
Mr Freeze comes back as an opponent for a single episode, in which the character is rather tragically killed for good .
The Royal Flush Gang is stated to be an old adversary of Bruce Wayne (in fact the current 'King' of theirs was even personally bested by him when he was young). Bruce tells Terry the story of Selina Kyle (Catwoman) after an episode where Terry falls in love with Melanie Walker, who is revealed to be a member of the Royal Flush Gang.
Ra's Al Ghul and his daughter Talia both appear together in a rather twisted episode.
In one episode Terry is injected with a potent formula of Vampire Bat DNA which splices him into a creature similar to Kirk Langstrom as Man-Bat.
An elderly Bane appears in one episode, revealing that years with Venom in his bloodstream have deteriorated his body so that he must be under constant care and life-support and is practically next to comatose.
The high school that Terry attends is named the 'Hamilton Hill High School', named after the mayor who ran the city during the events of Batman: The Animated Series.
Several modern villains even seem to be vaguely similar to classic Batman villains:
Inque appears similar to Clayface with the ability to alter and shift her form. It is later revealed that Inque's daughter has the surname of 'Clay'.
The terrorist spy 'Falseface' also seems to have similarities to Clayface, with the ability to mold his face like putty, much like Matt Hagen could before transforming into the monster he is more known for.
Spellbinder is a villain with characteristics similar to both the Scarecrow and The Mad Hatter.