If you reckon a bare minimal subsistence is living, then yes, the homeless have skills. I would argue this, saying that they basically leech off of what they can find, beg, or steal. Those aren't skills.

Skill is taking some logs, some rope, some knowledge, and making shelter. Skill is starting a fire without matches or a lighter. Skill is knowing where and how to find food - sans a dumpster in back of a fast food place. Skill is knowing how to stay warm, clean, and relatively safe no matter the weather.

Take away society as we know it, then the homeless are more than likely to be SOL than the average Joe.