A hook is something that benefits the college in some way – some sort of value added to the college. So a student who has some quality that the college is seeking more of has a hook.
A student may have a compelling story that aids in admissions of overcoming some sort of adversity or hardship – and that may result in favorable consideration of admission – but that is not the same as a hook.
I just want to add something else. You wrote:
Unfortunately it doesn’t work that way. Each college sets its own policies, and some colleges do a better job of supporting student needs than others. – so that may be something you want to research in advance about colleges.
Usually to get a 504 plan, there also needs to be recent diagnosis and documentation of the learning difference. Colleges can vary on their policies, but it is very possible that a student who qualified for 504 accommodations based on an assessment completed in 9th grade who receives accommodations all through high school will find that a college requires a new assessment (at the student’s expense).