My understanding of the 504/IEP distinction was that you could not receive "services" under the 504 plan. I believe that's more for the "freebies", like preferential seating, extendted time, and other things that really require little to no effort. I could be wrong though. And I'm speaking from an LD vantage point, and have no understanding of how medical issues work into things.
Students who qualify for 504 can receive related medical services such as injected medication at school (e.g. for seizures, diabetes, anaphylaxis.) I even know of a couple of people whose kids have one-on-one aides. These kids are disabled, but not necessarily in a way that substantially limits their ability to learn. It's more an issue of their ability to have safe access to school.
Schools don't like to provide more than "freebies" for 504 students because Section 504 is unfunded. But under the law, there is no restriction on the cost of accommodations. Legally, the school must provide FAPE (Free Appropriate Public Education) in the Least Restrictive Environment (LRE) to students, regardless of cost. Schools do get some government funding to pay for services for students with IEPs.