My friend Mike Riddle, well known for his award-winning Russian imperial stout, does use a lower attenuating Irish ale strain. He counters this with very high levels of roast malt and hops to try to balance out the residual sweetness. He also keeps the amount of crystal malts to one modest addition of dark crystal.
Even though this was at one time a British beer for a Russian court, the resurrection of its popularity in the United States means that a brewer has a number of fermentation choices. The only real must do is avoiding hot, fusel alcohols and an overly sweet finish.