Yes, as a matter of fact, that Lugia you always fear of not being able to OHKO, is, in fact, able to be OHKO'd, even without crits. However, don't get your hopes up yet. Let's look at some calcs...
252 Atk Choice Band Zekrom (+Atk) Bolt Strike vs 252 HP/252 Def Lugia (+Def) : 112.5% - 132.69%
252 SpAtk Choice Specs Kyurem-W (+SpAtk) Blizzard vs 252 HP/252 SpDef Lugia (+SpDef) : 100.96% - 118.99%
Just some examples on how much is needed to take down Lugia. Seeing that Zekrom boasts the highest Attack (Base 150) stat while still getting a SE STAB move on Lugia is quite amazing. And seeing that Kyurem-W has litterally the strongest Blizzard ever, and BARELY KO's Lugia, you can see why Lugia + Multiscale has become one of the scariest things to face in Ubers. Sure, it's possible to OHKO it, but don't think it will be easy.