If your tank is established all surfaces of it will have a bit of biological bacteria, so yes placing some media in the tank will allow it to seed.
In the actual tank most of your bacteria is going to be on your substrate, so placing it on the substrate will probably allow it to grow bacteria faster than if you just hang it against the wall of the tank or something.
Of course, media will seed faster in the filter than anywhere else because that is where your primary source of bacteria is. The filter also has the majority of the water flow so there's more oxygen to help the bacteria flourish.