"As a Ruby project, it unsurprisingly has vocal hipster fanboys."

This isn't my experience. Puppet Labs certainly doesn't promote their products as hip Ruby projects. That would be counterproductive, since their marketing is aimed at the enterprise sysadmin and his managers.

"in no time flat you’ll start seeing full blown Ruby programs intermingled"

On the puppet-users lists, questions that require writing Ruby are infrequent. For my repository, the filetype breakdown is

  $ find puppet/ -name '*.pp' | wc -l
  214
  $ find puppet/ -name '*.erb' | wc -l
  34
  $ find puppet/ -name '*.rb' | wc -l
  7