Yes, they are.
And you bring up an interesting point about the kinds of people photography on the street, that are possible.
1- People as a part of the urban landscape
2- People going about their business, completely unaware (or forgetting!) that they are being photographed.
3- People reacting to being confronted by the camera/photographer
4- People “allowing” their photo to be taken (going about their business, but aware of the camera).
5- People cooperating in an impromptu environmental portrait
But it seems the original question was on how to approach the situation when there are few people on the street, which makes it much harder to do type #2 (candids). Since they are hihgly likely to see you, the next best approach (besides shifting to types 1,3,4,or 5) is the make yourself invisible after they’ve seen you. They see you and yet don’t see you at the same time. Something about you makes them ID you as innocuous and they forget you’re there.
I did this a few days ago when I came upon a small street carnival in the parking lot of a local mall down here in South Florida. There were very few people at the carnival, just the workers and very few patrons, so there was no way they weren’t going to notice me.
I first made the rounds with my small camera (Panasonic GF1 with 20mm pancake lens) in my coat pocket and walked around as a tourist, played a few of the games the vendors offered, made small talk etc… Then I pulled out the camera and started taking photos of the rides (urban landscapes), moving around getting different angles of the architecture, moving very fluidly, giving rapt attention to the structures and shapes and not looking at any folks. After doing this for a bit, I was loose and relaxed, and everyone pretty much either igorned me, or felt open enough towards me that they wanted me to take their picture – perhaps they thought I was doing something artistic? who knows. But by this point, I could pretty much do whatever I wanted to. Move about, get close, take shots of people, things, landscape, whatever – as I was no longer “on the radar.” This mostly then became people photography of types 1,2 and 5 (above), with probably a bit of 4 as well.
But I guess my point is that if you can get into that fluid unselfconscious flow state, then things can start to happen, and one way is to approach the situation “obliquely” – with your body and mind and camera in constant motion – click-click urban landscape, click candid, click allowed shot, click-click cooperative street portrait, click candid, click urban landscape, all with fluid subtlety as in dancing and enjoying all of it. And when you get home at the end of the day, you’ll have your “street photography” shots.