What is the danger for Ceres of collision with other asteroids? In the context of possible colonization of Ceres, would not such colony be totally impossible because of high probability of collision of Ceres with other asteroids in the Asteroid Belt?
Sadly, a well referenced answer to this question likely lies behind academic publisher paywalls.
However, Wikipedia claims: 


  Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years.[63]


-Source for citation 63 has disappeared from the internet.

However, the Veritas asteroid cluster, and the Karin cluster reportedly formed by the collisional disruption of 140 km diameter and 25 km diameter diameter objects only 8.3 and 5.8 million years ago. These numbers obviously cast doubt on the Wikipedia claim.

This piece Small asteroid collisional characteristics from 2002 states: 


  Orbits of nearly 88,000 astreroids from the main belt are needed to find statistically one encounter within 1000 km distance during 50 years.


Naturally the more abundant smaller asteroids collide more frequently. In fact Hubble seems to have caught the aftermath of such an event back in 2010.

To answer the question. It seems Ceres will remain intact for some millions of years to come. But it does get hit fairly regularly, like the moon. If Ceres regularly took impacts large enough to preclude habitation, we'd expect to see co-orbiting debris clouds like the Veritas cluster, or in the 2010 Hubble images. We do not see such debris clouds near Ceres.