Yup, I'd always viewed being given man flesh was a special thing, a reward. I don't have the book to hand, but am pretty sure that "we ain't had nothin' but maggoty bread for three stinking days" has at least an equivalent in it. A clear case of Uruks not having an exclusive diet.
If Saruman had been outed earlier, I'm pretty sure he would have dug himself well into Isengard. Only the Ents it seems were fully capable of actually doing anything, and even then they couldn't get him out of the place. It would have likely ended up as a protracted siege with resources tied up in keeping an eye on him. There would have been no Helms Deep, no Ride of the Rohirrim, and Gondor would have likely fallen. By the time the White Council were really aware that the Necromancer was Sauron returned, he was already strong enough to move back to Barad Dur. And I think he would have been quite happy to leave Saruman stew - tying up resources in the west was the objective, and doing so would have had the same end result.