If you want to look at it that way, since I'm an SMCPS employee and I pay taxes that makes me own boss.
People have tried that argument many times and it just doesn't work. You pay taxes because you live in this state...period. That doesn't make you any state employees' boss...or in this particular case, county employees' boss. I can't being to count the number of times I've seen some uneducated redneck shouting that very same thing at a police officer as they're put under arrest. Doesn't work then...won't work now.
The federal government has little to nothing to do with education. It's run by the state governments and in most cases the local counties. Just thought I'd point that out.
And I'm also getting the feeling you know very little about how a unionized business/organization operates. SMCPS signed a contract with the union and part of that contract included a dress code. Attempting to force SMCPS employees to adopt a dress code outside of the one outlined in the contract would constitute a breach in said contract. I'm quit sure the union wouldn't hesitate for a second to take SMCPS to court over such a breach and would most likely win. So, in essence, you would be taking money away from your child's education attempting to pursue such a course of action.
If you actually wanted to do something about this issue you would have taken to advice I've already given you and gone and spoken to the site administrator for your child's school. He/she is your best contact point for raising such concerns.