Elementary School Nurse here. I typically get involved with IEP/504 only if there are medical considerations that may affect the student throughout the school day. I just came from and IEP meeting, actually.
If there is a significant medical history and/or the student will required accommodations due to that medical condition throughout their school day, I am asked to write a health assessment. I usually meet with parents/student and conduct and interview to gather detailed health history, obtain releases to speak with physicians, and discuss concerns that the parent may have if their child were to be enrolled in our school. My reports will summarize the health history and detail my recommendations/ concerns for that particular child during the school day. If there is a health assessment requested, I am invited to the IEP meeting to share my report. Sometimes daily treatments/procedures that will require the student to be out of class are entered onto the IEP. For a student with considerations that may not require leaving the classroom, I have the team note that there is an Individualized Health Care Plan that should be followed on the IEP.
Not sure if this helps, but this is my involvement in the process.