According to Troubleshooting Muse Form Widgets Used on Third-Party Servers, Muse uses PHP for forms. PhoneGap doesn't support local PHP running on the device, so you're out of luck. I suppose you could publish those forms on an external server, but you are apt to run afoul of Apple's policy against accepting wrapped web sites. Furthermore, you'd have to appropriately handle a bad/no network connection.
Only other option I know of would be to set up an external server with a web service that your local page could call via XHR (XMLHttpRequest). IIRC, Muse lets you embed scripts and the like, so that _might_ be an option, although you'd have to write the webservice and associated scripts, and craft the form by hand.