rake puppet:import:puppet_classes wasn't finding my classes, so I added a couple of puts to app/models/environment.rb to show what environment and modulepath it's looking. Now, even though my settings.rb says

--- 
:modulepath: /Users/eric/Sandbox/svn/puppet/etc/modules/
:tftppath: tftp/

This is what comes out:

rake puppet:import:puppet_classes RAILS_ENV=production
(in /Users/eric/Sandbox/foreman)
using environment production
scanning modulepath /Users/eric/.puppet/modules
scanning modulepath /usr/share/puppet/modules
Environment   old:1     current:1
PuppetClasses old:0     current:0

I was able to trick it with a symlink but this would be good to have working.