From this (mostly fine) article you linked to:
"Marx was a left-Hegelian, which meant he filed the serial numbers off God and called Him “communism”."I mean, no. That's a complete misreading of Marx. (Though perhaps one that was convenient to Stalinists or Maoists to continue to let breathe...).
For one, it would only apply to Marx in his 20s. Grown up Marx substantially threw out most of the Hegelian stuff, seeing it as superstitious nonsense while he studied commodity prices in the British Museum's reading room.
Or at least -- in his own younger-self terms -- he "turned it on its head" by throwing out the Idealist aspects of the dialectic. Even a traipse through the Theses on Feuerbach shows him rejecting all the transcendent forces of history crap.
I'd argue by the time we get to Capital the dialectic and the Hegel stuff generally is barely present.
If he is speaking of dialectic, it's mostly as "here's a way to look at history as it has happened, let's go poke at the contradictions and see what's in there" not "here's a recipe for how history works and from this we can predict..."
And back to Adorno, this is actually precisely what he is getting at in Negative Dialectics. Reinterpreting the "dialectic" as a non-Platonic, non-Hegelian process of looking at contradictions in reality and history but without expecting any kind of unification or resolution to a more perfect form. Living with the negative and the unknowable. Because the alternative, in Adorno's mind, was the path to Auschwitz.