There are a few different approaches to that kind of right hand speed:
I once interviewed Cuca Teixeira, who is Maria Rita's drummer, and asked him a similar question. He said that many Brazilians, simply from years of doing it, and the style of music they grew up playing, have really fast wrists. Some finger is surely used as well, but in general, many of these guys just have really fast hands. I realize that's not much of an explanation, but that is to say that I think this approach just takes a LOT of time to develop.
Check out how firm Cuca's hand is in this video:
This one isn't nearly as fast, but you can get a better look at his hands:
Edu Ribeiro, who is probably the fastest guy out there, uses this technique, although he seems to use more of a standard fulcrum - thumb and index finger directly across from each other.
Here is a video of him talking about this technique (starting around 6:30):
There are a lot of great videos of Edu playing with this technique on YouTube. Search his name with "bateria", as there are other Edu Ribeiros out there, and also check out some live videos of Trio Corrente:
You've probably heard of this before. There are a million videos on YouTube about it. Jojo Mayer gives a nice breakdown of it on his Secret Weapons DVD, and Gordy Knudtson has some good videos about it as well. In short, you play a stroke with your wrist/hand and allow the stick to rebound with your fingers relaxed. Then, as you are lifting your hand in preparation for the next stroke you close your fingers, creating another stroke.
If you are going to use this technique in a samba setting I suggest inverting the strokes. Play the downbeats with the fingers, and upbeats with the wrist. Because the wrist strokes tend to be stronger it will fit the samba style more, and you will feel the emphasis on "e, a, e, a" more naturally.
I just recently discovered a video of a Brazilian drummer talking about this technique. He also talks about a three note grouping idea which seems pretty cool. If you use the "Moeller pumping motion", as it's often called, you can achieve a string of rapid 16th notes, albeit with an accent on the first of every three notes. It actually fits the samba feel quite nicely.
*This Other Thing
I have no idea what this is called, but I've seen more than one Brazilian player use it. The fingers remain pretty stationary, while the stick is moved laterally, catching the cymbal in each direction. I've seen players use a sweeping kind of motion, while others do it with more of a twisting motion.
Here is a video of Cesar Machado (no relation to Edison) using this technique:
Marcio Bahia, who previously played with Hermeto Pascoal, and currently works with Hamilton de Holanda uses this technique quite a bit with brushes. Bahia is left-handed, so if you're a righty and trying this idea you may want to flip the hands. Start around 7:10.
I asked Marcio about this technique once and he said:
"It's a very good tool to increase speed playing 16ths on hhat on medium/up, or fast tempos...I really don't know [where] or [who] came first playing like this. We've learned just watching street smarted drummers doing, [which] I love it! And works so cool! Just relax your wrist and bounce it from side to side with sticks on a loose grip, not [tightening] them."