My college student took out a loan to pay for tuition, books, room and board. I co-signed the loan. Does this count as "provided more than 50% of their support"?

Yes, if you are responsible for the loan, you can include this as support. You can also include room/board, transportation, financial help for everyday expenses, etc. Every situation is different, but most full-time college students are still eligible to be claimed as dependents.