Saban's comments are interesting:
“I want to make it very clear that we will not condone any behavior issues in the future relative to Marcus Vick,” said Dolphins Head Coach Nick Saban. “Marcus acknowledges that he has made some mistakes, all of which has resulted in severe consequences for him. They have helped him learn that he will need to make much better choices and decisions in the future or risk similar consequences that could jeopardize his career as a professional player.
“As an organization, we did an enormous amount of research, including consulting with professionals in detailed, in-depth analysis to feel comfortable that giving Marcus an opportunity as a free agent is a risk worth taking. Marcus has made a commitment to this organization and our fans to represent the Miami Dolphins in a first-class manner."
from the official website