That's a good point and made me do some more research. The range at which B. cereus grows ends at around 50C -- the exact figure varies depending on the source. Generally, 65C seems to be considered safe. The "warm" mode of (some? check your manual) rice cookers is designed specifically to target that temperature range to avoid contamination[2][3].

[1] Gilbert RJ, Stringer MF, Peace TC. The survival and growth of Bacillus cereus in boiled and fried rice in relation to outbreaks of food poisoning. The Journal of Hygiene. 1974;73(3):433-444. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2130471/ Possibly the "seminal paper" when it comes to rice and B. cereus?

[2] https://en.wikipedia.org/wiki/Rice_cooker#History

[3] Manual for some random rice cooker on Amazon: "In Keep warm status, it will reheat to maintain the temperature at 73C" http://img1.midea.com/my/Local_Library/info_instructions/ins...