The CSS person doesn't need to know Sass in order for the project to benefit from it. At the very least, you could just dump the CSS in an .scss file and just use the automatic output formatting feature.

In my current project I take it a step further. I get the CSS from a designer, dump it in an scss partial, include that partial in the main sass/scss file where I then override and add styles. That way I can keep their CSS versioned and untouched while being able to automatically combine it with additional styles into a compressed CSS file.

The point is that there are plenty of ways Sass is incredibly useful even if the main CSS person doesn't work with it directly.

Obviously Coffeescript is a little different, but the advantage is that a Javascript developer is a programmer and it's not an unreasonable expectation for them to be able to get up to speed on Coffeescript.