It all depends on what its goal is. As a caretaker that serves as something that aids with their memory then I say yes. But as a companion type that helps the emotional side then I say not yet or no. LLMs are too prone to hallucinate randomly and there's really no there there. It's an empty bunch of words. It has no memory or feelings yet the person who has dementia is a full human being who falls in love and has feelings for other beings. Helping someone fall in love with or have feelings for words is not ethical in my opinion.