third party contact management applications for iPhone

Sorry if it is a stupid question, but I was wondering if the service will work with the third party contact management applications for iPhone, such as "WorldCard Contacts" for example? Will it sync all the data as it syncs with the native iPhone Contacts application?

It should, because those apps will be using the device-side contacts API to manipulate the contacts list.
Then the device will sync any changes to that list. But to be honest we've never actually tried this here.
OTOH we've never had user complaints that it doesn't work and I'm willing to bet we would have quite a few if it did not.
Next time I get a chance I'll try this out with the Facebook app, something like that.