Is this FizzBuzz code idiomatic Groovy?
Referring to 'Could I make use of any Groovy-specific features?':
You could use a Category to add a isMultipleOf() method to Integer. So you could write if (number.isMultipleOf3())
(see Groovy Goodness: Use Categories to Add Functionality to Classes)

class Multiple {
    static boolean isMultipleOf(Integer number, int multipleOf) {
        number % multipleOf == 0
    }
}

def foo = 5
use (Multiple) {
    if(foo.isMultipleOf(3))
        println "Fizz"
    else
        println "Buzz"
}