Full disclosure: I don't know much (read: anything) about Iowa or ISU, nor the hiring preferences of Iowa ChemE firms. So I'll try to keep my response general.
You should ask the ChemE program at any school you visit about their six month post-graduation employment rate.
I sort of doubt that, on a national level, that a degree from one school or the other makes for a more desirable job candidate. They are ranked nationally in undergrad engineering at 43 and 67. I glanced at the list schools ranked near them, and no offense to anyone, but they are basically in the same tier. Chemical Engineers are always in demand, so many employers care more about the candidates skills and knowledge than specifically where the accredited degree is from.
Things could be different on the local level though. Hiring managers, regardless of geography or discipline, can occasionally have biases towards one school or another. Again, I can't speak to how Iowa firms do things. But if he doesn't specially plan to stay in Iowa, or the region after school, then it really won't matter.
Some things that could affect employment would be if the undergraduate program has a co-op or internship program; which are usually feeders for employers. If co-ops are important to him, and one of those schools has a "monopoly" on potential internships, then you may want to consider that school. However most engineers easily find a job after graduation with or without an internship.
tl;dr Go to the school that's a better personal fit for him.