Yes, there are also the epigraphs from Way of Kings which say that Ati was a kind and generous man before taking on the Shard of Ruin, and we all say what became of him in Mistborn. Though I do believe that some of their original personality may be slightly left, which even so, isn't great for Odium as Hoid described Rayse as being one of the most crafty, dangerous and loathsome individuals he had ever met. So Odium, if still with a part of Rayse's personality, will not only be Hatred personified, but will also have a master plan more complex than Ruin's.