The original error looks like they have a really old version of haml... Did you try vendoring haml too?
That said, you really shouldn't be compiling stylesheets during test runs. They'll just slow down your tests for relatively little value. Assuming everything loads correctly, you can turn off stylesheet compilation in a Rails app by setting Sass::Plugin.options[:never_update] = true.
For the true test nazi's out there, compass comes with a TestUnit test case class for testing your stylesheets (ensures they compile and have something inside). I use it like this:
http://gist.github.com/234185 If other assertions are useful to people, please build them and I'll merge them in ;-)
Chris
P.S. Sorry your message sat in the queue so long, somehow I missed the notice. From now on, you'll go straight through.