DC serials like Arrow and Flash share the same universe.
Does Titans TV serial share the same universe as these serials?
In the words of Marc Guggenheim himself:
“Great question, again, above my pay grade,” Guggenheim replied. “I will say this, the one thing I’ve learned is 'never say never.' I could not begin to tell you how often we say to each other, ‘We never thought any of this was going to happen. We never thought we’d see all these characters. We never thought there’d be a universe.’
“So, never say never, but in terms of which characters be on which shows, what’s part of the universe, above my paygrade and probably that’s a good thing.”
But till now Titans is standing on its own feet without any crossover with any previous DC shows yet but will get a spinoff from same Titans universe soon called Doom Patrol.
Supergirl and Constantine were on the different network too in the first season but both get home in Arrowverse after there telecast channel cancel them. ANd on the other hand, Black Lightning is still an individual show till now.
Correct me if I'm wrong, I think Titans belong to new initiative DC Universe. You can see that from the intro in Titans. Series like Arrow and Flash are done by CW in collaboration with DC comics (under the title Arrowverse). There's a chance that they might merge the universes, but its highly unlikely as DC might want to continue the stories on their own.