There are no absolutes about tires. Yes, for light duty and careful use, you could certainly use passenger tires on the trailer and probbaly do so legally. But trailer tires are designed with different properties, supposedly including much higher UV resistance since they are assumed to be left out baking in the sun all the time and never garaged. (You'll see may expensive RVs with sun covers on their tires when they are being stored, because of that.)
I'd call my favorite tire company, not just the guy selling them, and see what they say about their own brand. Then look at the costs.
Guys who fly down the highway at 80mph with trailers that have 55-mph limits (on the trailer and tire alike) obviously aren't quite the same as guys who stick to trailer speed limits, check their air pressure, carry lighter loads less often and so on.
If your trailer is oversize for your load, and you're only making two sorts trips a year to store and launch the boat...passenger tires might be good enough.