Why would you worship or even pretend the second group exists if you have the first group of gods that actually talk back when you pray? I think people would demand a little more proof from new religions if the old ones had some
It depends on the gods and the worshipers.
One could be extremely dedicated to a particular ideal that none of the manifest gods advocates, and declare one of the rumored, silent gods as their patron. The active gods might not even mind, depending on how jealously they pursue worship.
The manifest gods might even talk about the silent gods. Zeus could brag about how he sealed the primal Titans away, before the creation of the world as we know it, or the pantheon could openly acknowledge that there where other gods, who helped create the world, but are uninterested in the prayers of mortals (Why someone would bother worshipping these beings could just be a matter of foolishness, or something deeper).
Others might come thirsty for the promise of power that the cult leader promises to those who learn the secrets of the gods of Outside, and willing to tempt the wrath of the gods of Earth to find it?
Then there's the simple fact that familiarity breeds contempt. Look at the greek pantheon. A lot of people, particularly those with very strict moral principals, would find Zeus a difficult man to respect, once they got to know him. What kind of physical incarnation of justice cheats on his wife, anyway?
If there is a single, active, obvious, unified pantheon, that fulfills the spiritual needs of everyone on the planet. No new religions or philosophies should be invented, as no one is going to be discontent enough with the current system to create something new.
However, that strikes me as being a pretty rare arrangement, the discontentment of people, and their exploratory natures being what they are.
Even on a world with universally active, objectively verifiable gods, that constantly correct any false doctrines, crazies and shysters will crop up preaching falsehoods. The gods would smite them for their lies, and draw their followers back into the fold (or simply destroy them, too) and that would be the end of it, but it would still be a pretty interesting thing to have happen in your fortress.
The other possibilities generally offer more verisimilitude, but the static nature of this arrangement would be nice for players who don't want the complexity of the other options, but still want an extra dose of the fantastic.
Customization adds a dimension here that brings something to everyone.