The two most major Brazilian MAs I know of are Capoeira, a martial art that is descended from Africa and was created by the slaves as a method to retain their fighting traditions by hiding them as a form of dance, the other is Brazilian Jiu-jutsu, as you mentioned. I think the most important thing to remember about all traditional MAs is that they take time to learn, if your character moved around a lot then he would constantly have to be finding new schools and instructors to train him. He most likely would spend a good portion of his time covering the basics that he already knew as the instructors established for themselves what he already knows and what he doesn’t. His skill would be decided mostly by how much time he spent training outside of lessons. Also, remember that MA training through a professional school can be both expensive and time consuming, expect the lessons to take up a half hour to an hour of his time no less than three to five times per week on regular intervals. If he is trained by a specific instructor on a personal basis, then it could be a lot more. If he is trained by his parents (the easiest under the circumstances) it may be his whole life like a lot of the kids I knew whose parents were instructors.
Decide this for yourself.
If he lives on the streets and you want a martial art that is specifically Brazilian, I’d suggest Capoeira. It involves dancing, tumbling, and other exercises that make it more of a stealth MA and he could make money off his skills as a street performer. It is a very unique style, however, so make sure you’re comfortable with writing it.
Other than that, it may be he picked up his skills from a non-professional source such as the local gangs and other forms of general street fighting. A character can still be an effective fighter from a non-traditional background, especially if he’s fighting other non-professionally trained combatants. It’s only when we get into it with professionals (of varying degrees of efficiency) that the shit really starts to hit the fan.
I hope this helps!