Appropriateness varies. If the abuse fanfiction is part of a story that ultimately aims to heal or show growth, it might be okay. But if it makes light of abuse or uses it in a way that makes viewers or readers uncomfortable without any redeeming qualities, it's not appropriate. Writers should be aware of the impact their work can have on the fan community.
Daryl Dixon isn't gay in the comics. The storylines mainly revolve around his adventures and struggles in a post-apocalyptic world, not his sexual orientation.