Sorry about the delay. First thing, Samba is basically 4/4 or 2/4, I really can't remember any song with odd time signature. If you do, please let me know! I like listening to odd time signatures.
The thing is, while being very "simple", Samba is also very complicated. As you noticed, you have a lot of different types of it. I'm not a Samba expert, but I dare to say that "real" Samba is kind of Lento like this, songs about love, everyday events and such.
There's also Bossa Nova, which is another type of Samba. The example is an old Samba performed by João Gilberto (he is credited as the creator of Bossa Nova). To exemplify my statement that Samba is simple yet complicated, look at the way the harmony, tempo, chord progression, voice and a "no music rules" way that he plays.
Today's Samba is called Pagode, it is faster, happier, it is music for the masses. On the other hand, there's a singer - Vanessa da Mata - that takes Samba as an "elite" status, just like early days Samba was (sort of). Here's a remix of a song featuring Ben Harper - Boa Sorte (Good Luck) - I believe that's the kind of thing you want to do (although the video sucks).
Unfortunately, I can't remember another artist that provides a performance that goes well with remixes.
Hope I helped in some way.
- What are the styles/main grooves played by Brazilian samba drum
Thinking in terms of percussion, do a Youtube search for "enredo escola de samba". Enredo is the story that the Samba schools sings, dance, homage during the carnival. It may be based on some folkloric history, real history, a person, the Samba school it self.
I believe that the "drum lines" are relatively the same, except for the transitions and such. Rio de Janeiro's carnival is one of the biggest events in our country (I don't like it, personally).Famous Samba schools includes: Mangeuira, Beija-Flor, Salgueiro, etc...
- Can you give me examples of them? (either by video, or by rhythm
The videos speaks for themselves. The Bateria (drums) is one of the most important categories and if they screw-up, it may cost the "Championship" for the school. As you'll see in the videos, the whole crew makes up the vibe. The costumes, the allegory, SFX, even the crowd. This video is a compilation of 50 songs, the uploader claims to be the all time Top 50.
- Where can I learn about how these styles are constructed? (Main and counter rhythms, using accents, how do they do deviate from straight, "Western" feel, which makes up the groove, what is essential in recognizing the groove, where you can "play" with the rhythm)
Though question. If you ask this to a member of the bateria he'll probably claim that you either "have it" or not. I can stress enough how complicated and yet simple Samba is. Is all about swing, knowing your timing, improvising. As we say here, you gotta have the manha (the only translation I can think of is "craftiness"). So, watch the videos, see how they "don't care" about keeping tempo, time signature, and yet they know exactly what they're doing. I believe that it all sums up to: Have fun.
PS: João Gilberto is a genius.