Yes

I too think it will. I have two large ceramic pots with clematis that have survived at least 5 winters without bringing into the garage. I have a thick layer of pine bark nuggets on top just to give it some added insulation. The old wine barrel should be more insulative than the ceramic pot. I am also in zone 6. The two I have are Elsa Spath and Carnaby. I have posted pictures under the title Clematis 2017.

Many Clems are hardy to zone 3.

The "oldtimer's wisdom" is that you should substract one zone when you grow in containers. So if you're in zone 6, you should look for plants that are hardy to zone 5. IME this is excessively pessimistic, but it will at least give you a guideline.

As buyorsell points out, clems are pretty hardy beasts -- often hardy to zone 3. So a zone 5 growing situation shouldn't bother them.