As most dahlias we plant are hybrids, for sure some will be hardier than others. But not to any huge extent. What is more critical than winter cold with overwintering in the ground is soil drainage. If you have a fast draining soil that does not become overly saturated in winter and you mulch well, many dahlia varieties are able to overwinter in the ground. But there is a limit determined by how deep your soil freezes. I wouldn't encourage this practice in zones below 7,

It also depends how mature the dahlias are. I lost every single seedling dahlia bar one, last year...but the older ones, with huge tubers, sailed through winter. Even so,they do better for me (usually) in the ground than in pots. Get them through the first year and they seem to do better. I only have limited dahlia experience but have found that the species I grow (d.merckii, d.coccinea and a so far non-flowering d,imperialis) all need to be lifted and kept dry under glass (lost several 3 years running and had to regrow from seeds every year, when my other seedling hybrids survived a UK winter (until last year, and a cold, wet March). Always hesitant to extrapolate universal rules from my experience though...but in general, dahlias are cheap and easy so always worth experimenting.