Not only was the Voom the "sub-atomic" power in the littlest cat's hat, it's eventual purpose was to cleanse the Red (pink) from the snow. The book was published in 1958, the cold war between the US and USSR was ramping up with over 100 combined nuclear tests in 1957 alone. Geisel was a vocal proponent of the US in WWII and eventually served in the US Army (as an animator).
By whom? To me, it was always a fun noise to say as loud and dramatically as possible, so to annoy my younger sister when I read the story to her. I'd always read it as a silly bit of deus ex machina employed to end the story, as we'd run out of letters in the alphabet.
Metaphor for a bomb? Maybe. But I doubt Dr. Seuss was trying to put forward the lesson to children that when you're out of ideas, the thing to do is blow it all up. I honestly think he was being silly for the sake of whimsy and amusement.
