Using AC rated relay in DC applications
A relay is not just a conductor, it's a switch. When opening and closing a switch under load, there will be an electric arc. When switching off a AC load, the arc will go away in the next zero-crossing. With DC loads, the arc stays there longer. Therefore, most relays have lower DC ratings if they are rated for both, AC and DC.

This relay will probably work with DC loads, but due to the missing rating, you don't know how long it will work under which conditions.