Kelly, if all you want to do is track how a campaign is performing, I'm not sure that you need the hidden form, extra javascript code, etc. The UTM codes will already be visible in Marketo, in the 'Querystring' tags (see my screenshot above). You can set up a search for them just by using that constraint in a SmartList, like in my screenshot.
This is how we track several of our third party campaigns (Adwords/SEM, LinkedIn posts, etc.) and it works quite well for our reporting purposes. We don't use any kind of hidden forms or extra javascript code.