It depends on whether D&D alignment means that the alignment saturates every thought, action, and behavior. That its impossible for someone chaotic evil to ever demonstrate a behavior contrary to it. I don't know that I've ever run a game that way.
Full disclosure, I've long abandoned the concept of alignment, but even in my games before I dropped it, it was more of an aggregate measure of the totality of one's actions and attitudes.
For example, you could have vampire that concealed their transformation and is still extraordinarily loving and fond of the mortal kin they left behind, while being sociopathic and evil towards anyone outside of that group. The aggregate of their alignment would be neutral evil. But towards their former family they could even demonstrate love and kindness. Though over time, their undead nature is likely to further corrupt their beliefs and attitudes until they became abusive or murderous even towards former loved ones.