Rather than contribute, yeasts vary in the degree to which they take malt and hop flavour away, I think.
I think the malts used and the alcohol, and perhaps the hops, contribute to the fruity/toffee flavour. Crystal malts give a toffee flavour. Fruitness can come from malts, hops and yeast. Fruitiness can be added by yeast, especially if fermented above 20C rather than below, and depending on the yeast strain.
A good experiment would be to split a batch and ferment with different yeasts. US05 leaves more malt and hop flavour behind but contributes very little flavour itself, temeperatures differences don't make much difference. Nottingham is similar and leaves a little more yeast flavour, but not much. I wouldn't ferment Nottingham above 20C though, personally. S04 does not attenuate as much as the other two, but clears well, and provides some fruitiness if kept above 20C. It may leave a FG that's a bit too high in a barley wine, perhaps.
Another dried yeast I've used successfully is Mauribrew Ale, which is pretty clean like US05, but provides some fruitness if you ferment at 22-24C, I've found. None of these yeasts are spectacular, but they are all good and reliable and do the job. I've made very good beers with all of them. If you want to go up the gears you could consider a liquid yeast, but you would need to make a yeast starter with a liquid yeast vial in order to make a barley wine strength beer.
