This Grommash doesn't know Thrall, and if he did, it would still be the guy who killed his mentor/friend/son.
Cenarius could be alive in this universe's Azeroth, assuming Broxxigar's role in the War of the Ancients wasn't key to defeating the Legion, but since the Dark Portal never opened in that Azeroth, he wouldn't even know of Draenor.
There is no Thrall in this universe, he just wasn't born.