dancers and running

In my trainging as a dancer – I was told that running was not beneficial for dancers.
Too much stress on the knees and the use of different muscles than those we were training to use.
Is this true and what is the current research or documentation on this.
I am a high school dance teacher and my administration would like the dancers to take the physical fitness exam.
I am in favor of the flexibility and strength portions of the test – but hesitant about the running. ( I do not train them in this ) so would like some professional advice concerning this issue. thank you