Doh! Shows what I get for posting a response to a book question when I haven’t read the book in around 8 years or so.
Dang it.
Well, in the version of “Young Zaphod Plays It Safe” that was included in the big book of all the HHGTTG stuff, they’re just aliens, and I was left with some confusion. But in the version included with “The Salmon of Doubt” (a posthumous collection of essays, H2G2.com prompts, unpublished works, etc.), the punchline is that “the missing escape capsule contained a ‘Reagan’ and that the planet in ZZ9 Plural Z Alpha must be made ‘perfectly safe.’” I don’t know how to account for the variation.