Due to the the decapodian mating tendencies (which include standing on beaches attracting their mates after which they die) I don't think they would be driven to cause life on other planets. However, it might be a good idea to send the mutants from the sewers. They could reproduce and improve their evolution within the constraints of that new environment.
On the abundance of extraterrestrial life after the Kepler mission Amri Wandel
Some recent calculation of the Drake Equation with estimates of the likelihood and logevitiy of civilizations
Related: The Great Filter and Planets in the habitable zone, the Drake Equation, and the Great Filter