Yes, it is a good idea to use radiator covers as a storage spot for decorative features to accentuate your home radiators and the overall décor of the room.
Radiator covers are designed to deliver heat outwardly into the space as opposed to above, so the top of the cover remains cool, making it an ideal place to house any decorative items you see fit.
For a deeper insight, browse our blog, How to decorate above a radiator.