When he wrote World War Z, Max Brooks did a great job pointing out what would happen not only to survivors in cold weather areas but zombies. I find it a particularly interesting point that the cold would tend to have a slowing effect on the zombies as that doesn’t often get covered in most fiction. In fact one of the disappointing things in the Walking Dead series is how they completely skipped over winter though they do mention it.
The danger frozen zombies pose is that they could stick around for quite some time. If conditions are right, if they thaw, or if the disease they cary with them survives for any length of time, it would be possible for multiple outbreaks to happen over the years with zombie numbers surging seasonally. Fortunately though the cold damages flesh and whatever brain is driving the body.