Was Eru or the Valar clueless?

[zb]

Kronos: You assume that the Valar worked only through the dreams. Is it not possible that they knew the particular family involved, and sent the dreams in such a way as to make Denethor most likely to send Boromir to Rivendell? As finwe said, "If Faramir was meant to go, then Boromir wouldn't have dreamt the same dream".

For an illustration of how Tolkien thought those of Faery* could manipulate history, here's an incident from "Smith of Wootton Major":

(Nokes) flapped his hand mockingly. 'If you've got one of your fairy friends hidden in the Kitchen, send him to me and I'll have a look at him. If he waves his little wand and makes me thin again, I'll think better of him,' he laughed.
'Would you spare a few moments for the King of Faery?' (Alf) answered. To Noke's dismay, he grew taller as he spoke. ... His face was young but stern.
'Old man,' he said, 'You are at least not my elder. And as for my better ... Do you challenge me now openly?' ... Nokes shrank from him, trembling. ...
'No sir!' he croaked. 'Don't do me a harm! I'm only a poor old man.'
The King's face softened. 'Alas, yes! You speak the truth. ... I will grant you your wish. Farewell! Now go to sleep!'
...
When the old cook woke again, the sun was going down. ... 'Ugh! What a dream!' It must have been that pork at dinner.'
From that day he became so afraid of having more bad dreams of that sort that he barely dared eat anything for fear that it might upset him ... He soon became lean ... But till his last year he could be heard saying to any that would listen to his tale: 'Alarming, you might call it; but a silly dream when you come to think of it. King o' Fairy! Why, he hadn't no want. And if you stop eating, you grow thinner. That's natural. Stands to reason. There ain't no magic in it.'

*meant in a broad sort of way, but including JRRT's calling Valinor "Faery" in The Hobbit