are可以省.这个句子属于倒装,因为从句的主语有了一个后置定语.
就象:Tom is taller than Peter (is).一样,
On the whole,ambitious students students are more likely to succeed in their studies than those (定语)(are)这一句中的are可省可不省.但由于这从句中的主语有一后置定语,than those with little ambition are 不仅不平衡,还极容易引起误会,所以就倒装一下.
其实完全可以省略.