This makes sense. All terrestrial plants use nitrates as their source of nitrogen. So any terrestrial plant with its roots in an aquarium holding fish will remove the nitrates to some degree (depends upon several factors). The roots only must be in the tank water, either in the tank itself or a filter. Some plants can be toxic though.
If there are fast-growing submersed aquarium plants in the tank, they will take up most of the nitrogen as ammonia/ammonium, unlike terrestrial which use nitrate. This means less ammonia is oxidized into nitrite and thus less nitrite is oxidized into nitrate.
The better situation here is to have thriving aquarium plants removing the ammonia/ammonium, if the nitrate is occurring within the aquarium. But if nitrates are present in the source water, the use of terrestrial plants will help.
Edit. Colin's post #4 is critical here too, I had missed that (never thought of it).
