I went to college not knowing there was even a such thing as IHSA or NCAA riding. Didn't take me long to find out my college offered riding for credit, though, and once they saw me ride they recruited me to be on the IHSA team. It was SOOOO much fun. It was the highlight of college for me. My team was like a sorority would have been - made a ton of friends, learned a lot, had a blast. I highly recommend it to anyone.
You are correct - IHSA is hunter equitation (the western side is western pleasure and reining). Don't let it turn you off if hunters or eq isn't your thing - it's just fun to be on a team. We had people with eventing, dressage, even saddleseat backgrounds join our team.