Is the booster segmented and are there O-rings between them?
A fair question. Making a tube long enough and straight enough without segmentation I think would be a daunting task.
An even better question might be: "Is the booster constructed in such a way that burn-through can't happen, no matter what the temperature?
Of course, this all is supposed to be in support of the Ares program, which explicitly keeps everything in a vertical stack, with the most sensitive items up top. This way, each element in the stack can have issues, but the odds of it destroying the sensitive item at the top is diminished.
After seeing how failure modes combined with horizontal integration has lead to 14 dead astronauts, it was a no-brainer.
“Is the booster segmented and are there O-rings between them?”
Since AFAIK these are five-segment SRBs, the answers are yes and yes.