Over on the Shakespeare section of Reddit, a question came up that I'd never seen before:
The general consensus is that no, Hamlet's not lying, and there's enough evidence to prove that (both in the text and historically).
It's fun to grab at a random angle like this every now and then, and re-examine bits of the play you might previously have been skimming over. During the conversation I wondered, "Once they lost Hamlet, why did R&G bother continuing on to England, anyway?" But then I remembered, their mission was to deliver that letter (which ended up being their execution order). They never knew that Hamlet was the primary reason for their trip. It does make you wonder what they were thinking when they watched a pirate ship sail away with the prince, though. "Oooooo! Claudius is gonna be *pissed*!"
Don't miss the later posts in the thread that focus on Shakespeare's use of exposition, and just how big a deal it would be to have a character lie while doing that. I personally like digging through the text, but that's mostly because at any given time I can find and search texts, whereas the historical stuff? I never know if there's some book I've missed that completely negates everything I think I've just learned.