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.
When writing Daryl Dixon abuse fanfiction, one should first consider the character's established personality. Daryl is a complex and tough character. Any abuse storyline needs to be in line with his overall resilience. Also, it's important to handle the theme sensitively as abuse is a serious topic. You can't just use it for shock value. For example, if it's emotional abuse, show how it impacts his relationships with other characters in the show like Rick or Carol.
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.