They should be fine in the summer as long as they get plenty of sun and water. The problem is the winter. The earth is a good insulator and you won't have that with the barrel (assuming you don't want to bury it). Potted plants are considered to be in a USDA plant zone that is 2 numbers lower than plants in the ground. They have a chance if you can provide enough insulation, but it may be a lot of work. They need a few feet of something like straw bales or dirt to keep the roots from freezing. 

I don't want to deal with insulating (and getting rid of the insulation in the spring) but want to grow some non-hardy trees. I keep them in pots and roll them into a garage heated to about 40 degrees. They go dormant, as will the blueberries, but need some water all winter to stay alive. If this method is an option for you, it should work. Otherwise they can stay outside with enough added insulation. 

See this from the Penn State for more info: https://extension.psu.edu/overwintering-plants-in-containers

This is from Maryland, where it is a lot warmer. But the growing info is relevant: https://extension.umd.edu/resource/growing-blueberries-containers/

Good luck!