Final answer:
The question is unclear about which specific riot it is referencing. Possible historic contexts include the political turmoil of the Hollywood Blacklist era during the late 1940s or the urban riots of the 1960s, with the mention of the 2011-12 arson unrelated to the direct actions of Hollywood figures.
Step-by-step explanation:
The question seems to be asking about specific incidents where Hollywood show-business types spent much of the riot but doesn't provide context for which riot is being referred to. However, one possibility is the infamous Hollywood Blacklist during the late 1940s, where a number of Hollywood actors and executives were accused of having Communist ties by the House Un-American Activities Committee (HUAC). This caused a significant disruption, and those blacklisted from Hollywood could understandably be considered figuratively 'caught in a riot', that of political and social upheaval.
Another historical context involves the urban riots of the 1960s in cities across America, reflecting social unrest due to racial tensions and other socio-political issues. While Hollywood figures likely were not the focus during these events, the film industry did produce works reflecting the civil rights movement and, as such, was connected to the broader societal upheavals.
Moreover, the mention of a serial arsonist in Hollywood during the 2011-12 New Year's holiday doesn't directly relate to where Hollywood show-business types spent during a riot, but showcases how statistical techniques can pinpoint social disruptions within a geographical area.