If I itemize deductions, it no longer matters if I am Head of Household or have Dependents, right? Ie, I am choosing to itemize over taking standard deductions.

Itemizing replaces the standard deduction, but dependent exemptions are a totally different thing. Whether you itemize or use the standard deduction, you still get a tax benefit from claiming dependents because those are totally different things.

Thank you for your response.  So then would this mean that itemizing replacing Head of Household or Standard Deductions, but the kids are separate exemptions?   I am trying to figure out my true impact of my ex spouse claiming her kids on her taxes (and my claiming no dependent, even though I have two kids and pay many of their expenses).

Not exactly.  The Filing Status is Head of Household or Single or Joint or Married filing separate.

Standard Deduction or Itemized Deductions is a separate deduction no matter what filing status you use.  You can take either the Standard Deduction or Itemized on Head of Household status.

To claim Head of Household you need to be filing Single or MFS and claim a dependent on your return,  If you are not claimng any dependents you cannot file Head of Household.