[Formendacil]

A couple different thoughts here...

Firstly, going back to the question of whether Gandalf is blameworthy here reminds me strongly of the philosophical Problem of Evil--whether God is blameworthy for allowing evil to occur, except Gandalf has (I think) the legitimate excuse of not being an omniscient, omnipotent being--powerful, but most certainly not unlimited, and although Gandalf has a certain amount of prescience denied other beings, he is still a Maia taken form as a Man, with most (if not all) the limitations that implies. A defensible case can be made, I think, that Gandalf was not aware that Saruman was in the Shire.

But even if Gandalf was aware, this does not mean he had to step in. One of the theodicies (that is, arguments that attempt to explain the Problem of Evil) is to suggest that God allows evil things to happen because this is necessary for our free will to function. I would suggest a similar explanation here: that Gandalf may have known indeed that Saruman was in the Shire, but because he had stripped Saruman of his staff and powers, he knew that Saruman could not pose more of a threat than the Hobbits could handle--and therefore he stayed out of it. Indeed, if you look at Gandalf's actions throughout the Lord of the Rings, he tends to use his power chiefly and most obviously against enemies that truly outmatch others--such as his battle against the Riders on Weathertop, or again against the Witchking in Gondor, or the obvious one against the Balrog. But where the enemy is one that others are capable of handling, Gandalf tends to step back into an advisory role, as when preparing for the assault on the Black Gate.

In the case of the Shire, Gandalf would be in a position to know, if anyone would, whether or not the Hobbits were capable of action against Sharkey and his villains, as indeed they proved to be, and it strikes me as a reasonable hypothesis that Gandalf would have abstained from interference out of respect for their own maturity as a community and people to be able to handle their own problems.