No. Unless the female had her own litter and accepted it, which has happened. It's more likely that they would view the mouse as food. Rats are predators, mice are prey.
Like it was said above your rats are predetors. They could get along with the mouse for awhile, maybe even months (it's happened) but one day one of your ratties instincts could just take over and before you know it your mousie is dead.
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