Not in this case, for two reasons. First, "Uniting for Peace" is a General Assembly action, which is not subject to a Security Council veto. And second, parties to a dispute in the Security Council are not supposed to be permitted to vote. The US shouldn't actually be allowed to veto a Security Council resolution against toppling Saddam. Of course, it never actually works out that way—in the Suez Crisis, for example, France and Britain went right ahead and vetoed resolutions involving them, because at the end of the day the UN is utterly unable to impose its will on anybody, even when it comes to basic parliamentary procedure within itself.
In any case, this is all meaningless. If Cameroon wants to declare war on the United States, it can go right ahead. If Vanuatu insists on embargoing the US, well, that's its right. If Belize wants to close its borders to US visitors, so be it. And if China or Russia really wanted to rid the world of a few billion in surplus population, they could trigger the Apocalypse with the push of a button. What international "law" may say on the subject is irrelevant, because the ultimate enforcer of that "law" is the United States itself. If a country is prepared to risk our wrath anyway, whether they receive the UN's blessing to do it is immaterial. Our security lies in power, not paper.