It appears that the Vietnamese did not discriminate based on race in terms of capture during the Vietnam War. But, the vast majority of the prisoners they kept weren't soldiers, the vast majority of them were pilots that had been shot down by PAVN anti-air fire. There were around 15 prison camps that operated at any given time, and most of them were in close proximity to, if not directly in, Hanoi. The most famous of these prison camps, Hòa Lò, or the "Hanoi Hilton", quickly became infamous for it's brutal treatment of prisoners.
The camp itself was a French prison camp from the days of French colonial rule in Vietnam. It's pretty difficult to describe an overall design for the camps, as no two camps were the same. Every one had it's own unique design and level of intensity regarding prisoner's relations and torture. The Vietnamese used just about everything in the book to break people, they would bind prisoners with ropes and stretch their joints, beat them, use intense solitary confinement, and malnourish their prisoners. The end goal of torturing their prisoners was not just to extract information. The Vietnamese were more focused on recording American prisoners making statements that were directly anti-American that they could publish and spread as propaganda.
Even though all of the American POWs were released in 1973, the release is shrouded in controversy to this day. 591 American POWs were released to go home on January 27th, 1973, but the US still had a very sizable number of servicemen still listed under POW/MIA. A document found by Stephen Morris that supposedly had correspondence between Tran Van Quang, a Vietnamese general, and Vietnamese intelligence in Hanoi was found that stated that there were upwards of a thousand prisoners in Vietnam was unearthed in 1993. The document was declared a forgery by the US government officially, but there were still a good amount of people who believed it's legitimacy, including former Secretary of State Henry Kissinger. I cannot state for certain what the exact number of POWs were in Vietnam, simply because there is so much misinformation and propaganda surrounding the captured's statements and the varying attempts at politicizing the prisoners from both sides.
Prisoner Of War: Six Years In Hanoi by John "Mike" McGrath is a very solid source on the inner workings of the "Hanoi Hilton" from a first-person perspective.
This gallery from PBS has several drawings done by McGrath, as well as information concerning your question about prisoners being bound. It also illustrates the tap code that the prisoners used to communicate, as well as the forgiveness towards each other and the sense of companionship they all shared.
This article from the Vietnam Archive at Texas Tech takes a very bold stance on the POW/MIA issue, but ultimately contains valuable insight and facts on the issue.