TL;DR: My 2001 Pontiac Grand Am SE had a flashing check engine light and I found oil in the coolant.
A family member took the car to a mechanic this week. He checked it over and said that it was a problem with the ignition (which he fixed). As I didn't drop off or pick up the car personally, I don't know exactly what was wrong with the ignition, but I'm wondering if I should get a second opinion from another mechanic. It seems off to me that all that was wrong was an ignition problem, given that there was oil in the cooling system, and I don't want to drive around a car that could go at any time.