Version control is a tool for tracking changes to code. It can also serve as great backup tool.
Yes, we use Git.This is the best answer. Best because Drupal uses Git for it's own management, so they're more likely in tune with Drupal best practices. Yes, we use a SVN/CVS/Mercurial/etc.This is acceptable. I won't go into the different options here, but anything is a good sign. No. This is a bad sign. This means they're far from an enterprise company. It means thing aren't being done to what has become an industry standard. It means there is greater chance for things to go wrong, and a tougher recovery if they do.