Yes, he could be. There are many fanfictions in the Supernatural fandom, and Theo Raeken might be a character in one of them. Fanfictions often introduce new or existing characters from related shows into their own unique storylines.
Isolation is also a theme. When Theo is hurt, he is often isolated either physically or emotionally, which makes his journey to recovery more difficult and interesting to read about. He has to deal with his pain on his own most of the time.
He could be a villain. His complex personality might make him a great antagonist in a Supernatural fanfic, causing trouble for the Winchester brothers or other main characters.
One great Theo Raeken hurt fanfiction is 'Broken Wings' where Theo endures a lot both physically and emotionally after a battle. It really delves deep into his character.
In most 'hermione and theo fanfic', Hermione is often depicted as highly intelligent, strong - willed, and very passionate about knowledge and justice. Theo, on the other hand, is usually shown as a complex character. He may be brooding, having a troubled past from his Slytherin upbringing, but also having a hidden depth of kindness and a desire for something more than the typical Slytherin values.
Theo Galavan is actually an original character created specifically for the TV show and doesn't exist in the comics. The show's creators came up with him to add a unique element to the story.
It depends on how you define 'real'. Some of his stories might be based on real experiences, but they could also have elements of exaggeration or fictionalization for entertainment purposes.