My best/least worst comparison to Vermont would be places like Stroud or the Peak District where Labour are competitive in places that they aren't elsewhere or to be expected on pure demographics. Therefore, I think Vermont could be competitive between Labour and the Conservatives, though I concede its the sort of place that the Lib Dems could do well and the Greens above average.
AIUI, the Labour strength in Stroud since the 90s has been partly down to the personal popularity of the slightly odd David Drew. Before he came around, it had been perpetually out of reach for Labour, and the Liberals even took over second place in the 80s. It's not really clear, at least not to me, how much of it will stick with Labour once he's no longer the eternal candidate. The Greens are already sniffing around the place. All that said, I suppose the reasons for social democratic (as opposed to Democratic) electoral strength in the real Vermont are not that different.
Stroud and the surrounding villages are quite industrial and as such have always had a decent Labour base. Drew is certainly effective at squeezing the hippy vote and does have a personal vote, but I don't think there's very much reason to believe it isn't winnable without him.