Let us say I've got a WordPress website which will sell WordPress Templates.

I wish to assign roles. For instance, Partners which will upload their templates. And I must split the revenue: 30% for site owner and 70% for partner.

Can you really do that with WordPress? If that's the case, what plug ins will let me make this happen?

In my opinion MarketPress has got the functionality for your. States it will around the home page. Pretty flexible and robust wordpress plugin, I lately authored a mod for this.