Absolutely. Although it may not be seen as “best practice” there are times when it makes sense. For instance, some school districts prefer medical issues to be on a 504 instead of an individualized health plan, particularly around issues such as diabetes or allergies. Additionally, during a student’s last year of school it may make sense to create a 504 in preparation for college since an IEP does not typically follow one to college.
There is nothing in the law preventing a student from having both plans simultaneously.