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Yeah if you're using another regulator when stepping down from 12V to 5V you're probably fine (I'm no expert either) but if someone's getting 5V directly from USB (as your wiki suggests as an option), looks like they should use a regulator.
I just noticed your wiki says "The 3.3 V outputs are not sufficient, as the board requires 5 V." which contradicts my experience. What's the source for this sentence? The MCP2515 datasheet says it can take as low as 2.7 V.