Typechecking and Typechecking are different things. You have a full spectrum of different ideas when you look at type systems. You can have fully manifest typing (as Python or Smalltalk have) and still can have usefull type informations - by using type inference. So actually the ASTs a refactoring tool can be enriched by information that goes beyound the source. Type inference isn't thant new - several Lisp implementations use it to optimize their code. Of course you could it to make better refactoring tools, too.
Of course it is more problematic to have enriched information for refactoring in fully dynamic languages with strong focus on manifest typing. But it's still up for discussion wether that really is needed. By gut feeling I would go with James Robertsons assertion that static typing in the long run doesn't help. But then, I do Smalltalk since somewhere in the 80s and Lisp since the end of the 80s, so I am a bit biased.