Does dechlorinator remove ammonia?

Some of them do, as stated on their packaging. The main reason for this is because when dechlorinators are used to treat chloramine, they only react to the chlorine part of chloramine and not the ammonia part. The remaining ammonia ions left in the water are toxic to fish, so some dechlorinators — such as Aquarium Co-Op Easy Dechlorinator, Fritz Complete Water Conditioner, Seachem Prime, and Kordon AmQuel — contain extra chemicals that temporarily lock up the ammonia into an inert state (i.e., ammonium) for up to 24 hours. During this time, the ammonium can be consumed and further broken down by beneficial bacteria in your aquarium and filter.

For more information, read the full article on dechlorinators.