Does Grafdigger's Cage prevent Collected Company from finding creatures?

Grafdigger's Cage states that creature cards can't enter the battlefield from libraries. Collected Company instructs you to look at the top six cards of your library and put up to two creature cards from among them onto the battlefield. Because the Cage prohibits creatures from entering the battlefield from a library, any creatures you find simply cannot be put onto the battlefield.

This is governed by replacement effects and restriction rules. Under CR 614.1, Grafdigger's Cage creates a replacement/restriction effect that modifies or prevents the event of creatures entering the battlefield from a library. Collected Company's instruction to place creatures onto the battlefield is simply blocked by this restriction — the creatures stay wherever they would have gone (in this case, they remain in the library, as Collected Company has no fallback zone to put them).

Practically speaking, when Grafdigger's Cage is on the battlefield, resolving Collected Company still lets you look at the top six cards, but you cannot put any creature cards onto the battlefield. You then put all six cards back in any order. The spell resolves, but produces no creatures. You do not get to keep or draw the cards.

Concrete example: Your opponent controls Grafdigger's Cage. You cast Collected Company, look at the top six cards of your library, see three excellent creatures, but you cannot place any of them onto the battlefield. All six cards go back on the bottom or top in any order (per the card's instructions), and no creatures enter play.

This interaction is well-established in tournament play. The Cage was specifically designed to shut off effects like Collected Company, Chord of Calling (via convoke into library), and similar library-to-battlefield effects (CR 400.1, CR 614.1).