I know as a GM I can allow anything, but rather than create another special rule I want to see if there's anything RAW or RAI that already covers this. Ex:
The party comes upon signs that point to a barghest in the area; its tracks mingle with goblin prints, said tracks shape change, and since its been seen by some fearful hunters they've got a rough description.
Now Knowledge: Nature is going to tell them it's NOT a natural creature, but none of the players in this scenario has Knowledge: Planes. Since goblins sometimes worship these things and these goblins have dwealt in the region for centuries could they sub Knowledge: Religion or Local for Planes?
So I guess there's nothing RAW/RAI on this one.
I don't believe there is anything that specifically covers this sort of thing, though if more than one knowledge skill can apply to a particular scenario, such as this, it is completely legitimate to allow checks other than the standard "Identify a monster" check. Just make sure that you change what their character knows to reflect what skill they used. For example, if they used religion to identify a barghest as a center of goblin worship, you might say something along the lines of "You have heard tales of goblins worshiping these strange wolf-like creatures. They are said to be otherworldly relatives of goblins with strange powers who come to our realm to gather goblin followers" rather than "You remember hearing of the barghest, a strange creature from another plane that makes it way to the Material Plane to hunt and grow in power." It's all up to you.
I would have to say in this case no. The reason is there are a ton of things that worship other creatures so if you allow that pretty soon the only knowledge you will need will be religion. A couple of examples are kobolds worshiping dragons, and pupwampies worshiping gnolls. add that to the fact that a lot of outsiders are also worshiped mainly demons and devils makes an even stronger case.
If you did allow knowledge religion to be used this way then the creature should at least be able to grant spells.
I enjoy allowing innovative uses of skills, and would give a brief overview of a creature if there was such a plausible link for a substitute skill that a player thought to ask for.
That said, a party without an extraplanar expert is asking for trouble in this arena.
My call would be that you could sub a knowledge for another knowledge, but with modifiers.
For your example, I would say, just to throw out numbers, if it would be a Knowledge: The Planes DC 20 to recognize the tracks as a barghest, then it would be possible to recognize the tracks based on Knowledge: Religion. However, it would not be a DC 20. It would be the DC to know that goblins worship things called barghests, we'll call it 20, plus 4 to represent being familiar enough with the creatures to recognize what their footprint might look like, plus another 4 to connect a religious idol with identifying a monster. If it were a Knowledge: Local, I would say that it'd be DC 20 plus 4 to recognize the feet plus 4 to realize goblins in the area worship them without knowing about religion plus another 4 to connect all those facts. So it would finish with a DC 20 Planes, DC 28 Religion, or a DC 32 local.
Additionally, if I have a character that has multiple applicable Knowledges, I would argue that they could make checks to eliminate certain variables of a DC, but only make one appropriate knowledge check. For instance, say a character doesn't have Knowledge: The Planes, but they have Religion AND Local, but their Local is higher than their Religion. I, as the DM, would roll those checks for them, but as per logical reasoning, I would roll a DC 15 Religion check for them to know that the local goblins worship barghests, which eliminates the plus 4 they get on their Local check for having to know that without Religion. So now I roll a DC 28 Local check for them.
It's a little complicated, but as far as I'm aware, there are no RAW on the subject and that is my logic on the matter.