I would also like to point out that, while the proxy approach is the best route, for end to end validation, you can at least verify the client side functionality of Omniture, that it is setting the correct values by running javascript code to return the variable values for you to assert against. The exact variables depend on your Omniture setup/implementation, consult your Omniture expert in your organization. It would go something like this:
String value = ((JavascriptExecutor) driver).executeScript("return scode.prop43;"); //or scode.eVar54, etc.
You would extract or query these variable values after you know they have been set. e.g. for page load events, they should already be set after page loads. for click and other events, you have to trigger it by clicking the relevant element that would then have Omniture set the value. Then you query the value to assert against.
Note however, that with this technique, on some events that take you to a new page (e.g. a page load that redirects to another page, or a click event that loads a new page), you may not be able to effectively query the Omniture values - only works when you are on the same page and not a new page. So in this case, you would need the proxy method to verify when there are new page (redirects).
We've used this javascript method in our organization since we don't deploy proxy servers (yet).