No. Different species should not be allowed 'play time' together. Neither group will benefit, and you run the risk of injury to your pets. I've seen a rat chase an adult rabbit, and my older (neutered) male Tsume would actively chase/bite by dogs if they happened to be near him while he was freeranging. Rats can be territorial little buggers .
Just as a side-note, rats are pretty susceptible to diseases and illness, and letting them roam free-range outside is asking for ticks, fleas, and the infections and disease that come with those creatures.
I would also like to see the fence capable of holding a rat.
Just be careful I guess, and don't be surprised if you get itchy rats in the near future.