Yes and no. Yes, because there were large polities in the Amazon as described. No, because the descendant populations aren't hunter-gatherers. Modern indigenious populations in the Amazon, like the Yanomani and the Kayapo are largely agriculturists like their ancestors - who had been practicing agriculture for thousands of years. Crops such as cassava, peanuts, and possibly sweet potatoes (there's a debate over whether sweet potatoes descend from a Central American or an Amazonian ancestor, or perhaps both) originated in the area. By the time of European contact, they had also acquired crops from further afield, such as maize from Central America and potatoes from the Andes. Of course, lacking domesticated animals, these populations traditional have supplemented their agricultural diet with wild game (or raising captured wild animals, such as turtles or tamed peccaries).

Ancient Amazonian farmers invented terra preta, an artificial soil that - unlike natural rainforest soils - retains its fertility under agricultural practices for far longer. Sadly, the techniques used to create this soil seem to have been lost a few centuries before European contact (the soil retains its fertile for so long that once enough had been created it obsoleted itself). Maybe someone will be able to recreate it in the future, because it would be a huge boon to food production in the tropics and help slow the destruction of the world's rainforests.

While I'm on the topic of things the ancient Amazonians invented, I should also mention pottery. The oldest evidence for pottery in the Americas come from the Amazon and it appears to have spread through the tropical regions of the Americas from there. In the temperate regions of North America, pottery was developed independently sometime later but before the wave of Amazonian-inspired tropical pottery reached that far north. Here are two examples (1, 2) examples of pre-Columbian pottery from the Amazon. And, of course, modern indigenous peoples of the Amazon continue to make ceramics.

Many of these large Amazonian societies existed when Europeans arrived. The expedition led by the conquistador Orellana in the 1540s from Andes to the mouth of the Amazon provides our earliest historical look. For example, he encountered the Omagua who controlled a 300-500 mile stretch of the middle Amazon. One Omagua town had an estimated 8000 people, while another stretched along the Amazon for 20 continuous miles, and a third had a warehouse full of ceramics waiting to be sent out for trade. As large as Omagua was, the people along the Amazon agreed that the Ica to the north were even larger and stronger. Orellana didn't encounter the Ica and specifically avoided too far away from the river (he didn't want to split his forces or commit to an overland expedition), but he did chance upon the roads the Ica built through the forest. While not about the Omagua / Ica region, you might find this article about the pre-Columbian roads in the Bolivian Amazon interesting. Further downstream, the vicinity of modern Santarém also densely populated by the Tapajós, who were said to be able to dispatch a force of some 60,000 archers in the early post-Columbian period. At the time of Orellana, his contacts in the area said they were led by a queen called Conori who ruled from further up the Tapajós River. Though Orellana never met Conori, it was after this warrior-queen that the Amazon was named. On Marajo Island, at the mouth of the Amazon, there was another large Amazonian society. The largest community there, now the archaeological site known as Cutamins, had a population of an estimated 10,000 people. Cutamins had declined prior to European contact, but the Marajoara were still numerous on the island and neighboring areas, and divided into several smaller competing polities which resisted Portuguese influence until the mid-1600s (when they were known as the Nheengaibas, an exonym applied to them by the Tupi).

Ultimately, these large Amazonian polities were highly disrupted by European diseases and warfare with Europeans and other Amazonians. In this turmoil, the Omagua refugees headed upriver to join with others into a coalescent Cambeba identity. The Marajoara were eventually defeated by a combination of Portuguese invasions from the south and Carib invasions from the north. The Tapajós identity faded away due to a combination of emigration to other communities in the Tapajós and Xingu River valleys, assimilation efforts by Jesuit missionaries, and warfare with neighboring peoples like the Wuy Jugu.

Unfortunately, I don't know of an English translation of the chronicle of Orellana's expedition, but River of Darkness is a good substitute if you want a more detailed look into what the earliest Europeans in the area saw.