Connected in the sense that they interacted, and that what we did to Riven may come up when Savathûn appears down the line.
We know that Savathûn visited Riven, and as a result Riven “takes a new shape”:
She knows that though I am [Taken], I am beholden to no one. So I ask her if she wishes to take up those strings.
She does. And I take a new shape. My cage loses its purpose.
I can tell this is not a part of her grand design. This is an introduction. She is at play.
This “new shape” is presumably what Mara was talking about in the Reverie Dawn lore:
This creature is all teeth and broken promises, transformed by the expectations of another scheming, secretive sister.
Additionally, a Taken can have free will while simultaneously being under the control or influence of someone else. Like Quria, Riven was both Taken and had some measure of free will:
I am [Taken], and I am beholden to no one. Nothing.
And Quria supposedly gained a great amount of power post-Taking, as Toland says:
“Quria is the key. The mind simulates Oryx and thereby masters the power to take, but of course Quria is no power onto itself.”
So, even if Riven is Taking other enemies herself, that doesn’t completely strike out the chance that she’s connected to Savathûn, Xivu Arath, etc.
I’m not sure what card you’re referring to. Oryx says this in XLVIII:
When I make my Taken I make them closer to perfect, I heal their wounds and enhance their strengths.
And Ikora speculated on the origins of the Taken in TTK:
The process is simple: an aperture opens, like a jaw, and swallows a living thing. It passes into — another place. Later, it returns. […] Are the victims devoured, and replaced by simulacra? Husked out and filled up? Is some mathematical operation conducted on them, translating them from one shape to another?
But I can’t find a BOS card that has Oryx explicitly explaining the process required to Take.