Should you activate the slider and pay for it separately, even though you already bought the theme, which uses it?
The short answer is NO, you don't need to.
Longer answer is:
We bought an extended license keys for all our themes, which use them. This means, that you don't need to buy it on your own, you've already payed for it when you
purchased our theme.
Of course there are some limitation. The license does not allow users to sell the plugin further or use it with other themes for example.
But with purchasing our theme, you have the right as our client, to use it freely on our theme. You can simply ignore the notices.
Updates of the plugin are also available. Please check the section how to update the Revolution slider.