There are several methods to check this, I would suggest httpfox or fiddler for one time validation, but newer tag monitoring tools like Qmon for continuous validation of your sitecatalyst implementation.
You probably want to use a tool that validates in realtime; crawler or simulation tools are not going to work for your goal. Also you want to set up the validation rules once, and let a tool check the set of validation rules on each google analytics request afterwards (then you are validating 100% of your data). This reduces regression testing time a lot.
Take a look at Qmon, it takes a whole new approach to data quality: Qmon - easy webanalytics monitoring.
PS. I'm working for Adversitement, who invented Qmon
