It was teased that Batman #9 by Tom King and Mikel Janin would have some kind of tie in with the whole Watchmen-in-the-DC-Universe thing. If so, I'm not sure.
The closest I can get is Bane sitting on skulls, which is rather Black Freighter-like.
And certainly, the Psycho Pirate may be a way between realities. But the biggest reference to the DC Universe Rebirth #1 one-shot is… well, you remember this supposed time traveller from the future who seems set to tease the Legion Of Super-Heroes?
That's her. And what she had on her…
Well, in Arkham Asylum, she's there. Anonymously, tagged as "Jane Doe".
And making a very familiar symbol in the condensation…
But no, there are no Watchmen signs that I can see. Although there is reference to another work written by Alan Moore, as Batman traverses Arkham Asylum looking to put together his own version of the Suicide Squad to take down Bane.