Solid riding experience: This all depends on what level you're riding at now, the college you attend and what you hope to gain from it. I've heard of people saying that riding for their IHSA team was a fantastic experience and those who hated it with a passion.
The quality of IHSA programs vary greatly. Some schools treat the IHSA teams as an actual sports team (and thus help with expenses) and some schools treat the program as a club or intramural team with little to no financial support. Some colleges have their own barns, horses and on-staff trainers. There's also the smaller teams who train out of local barns that must pay for their lessons. Some barns are great and some barns are not so great.
And I'm assuming you're familiar with the showing format? Some people never warm up to the idea of investing all this time and money so they can sit on a horse for a total of about 12 minutes. (10 minutes flat, 2 minutes for fences)
Scholarships and aid: I wouldn't count on it. At least not in the traditional, 'Here's money to help pay for college.' IHSA offers a few smaller scholarships to current IHSA riders to help with riding expenses. And I've heard of a few riding programs to do the same, but again, it's to current riders. Not prospective riders. (That being said, there may be some schools that do, but I have not heard of any personally.)
Most, if not all, athletic riding scholarships are for the NCAA programs. And even then, the competition is very intense. A lot of these kids ride in the big A/AA equitation shows.
(The cool thing about IHSA is that riders of all levels can compete. From walk-trot all the way to advance/open.)
Your best bet is to contact the colleges directly. Try and talk to current team riders, meet the coach and see if it's a program you'd like to be part of.
Now, my experience was a great one. The college I went to had their own barn and a great trainer that was also a 'R' rated judge. They even offered college credit equestrian classes. I took one of these classes as a beginner and was recruited as a walk-trot rider for the team. We had 2 classes (lessons) a week, one team practice and we could practice ride or trail ride anytime a suitable horse was available. (The downside was that this class cost an extra $1,500 a semester and if you wanted to be on the team, you had to take riding as a class. It was totally worth it, but even now, it was kind of pricey.)