Interesting memory...although it might not be as precise as it sounds. The thing is that Super Monkey Ball was not released for the Dreamcast [and it COULD have been, as the original Monkey Ball game was for the NAOMI Arcade Board, which was based off the Dreamcast], so either you might have actually played this in another platform [GC, PS2 or Xbox], or you played the only game I remotely know that's similar to Monkey Ball for the Dreamcast, which is a homebrew port of the free game Neverball, which is inspired by SMB.
Definitely have to delve deeper not only into the Super Monkey Ball original levels themselves, but also into this Neverball game...as unlike SMB, it is possible to play with a keyboard and still be able to deal with the harder levels...for the most part.
In any case though, glad to see you around here, and thanks for leaving a comment :]
I think you are correct about my memory. I believe I played it on PS2 but regardless it was a fun game although the audio did kind of get on my nerves after a while. If I had people over it was a "go to" to put on because unlike a lot of other games you don't really need to know anything about anything in order to have a try.