Durkula apparently is looking for something a bit more specific than that, given that he's apparently fishing for an excuse to drag Roy out after them. Given that we have a situation where a large number of high-ranking clerics all gathering, ostensibly in secret (judging by the fact that they kept largely mum about it without any celebrations or feasts, and the only person willing to talk about it was a single newly-minted acolyte who apparently didn't know she wasn't supposed to speak of it), and including at least one high priestess, I wouldn't actually be surprised to find that all of the visiting clerics were high priests or priestesses, or at least their closest and most powerful confidants. Hel (and by extension Durkula) knows about whatever is happening, but she didn't have any clerics as powerful as them before Durkon since they kept getting killed by adventurers, so she couldn't participate. As Roy notes, the Pinnacle Mountains are a haystack covering 2000 miles/3200 km; that wouldn't be "Good enough" unless Durkula already knows where the needle is hidden or has a really good magnet. It's described as some sort of pilgrimage, which seems to suggest that there's a specific, religiously-significant destination they're heading to, but it's apparently one that Durkon himself would not and does not know about, given that Durkula's going through this whole song-and-dance instead of mentioning to Roy that, hey, there's this cleric retreat in the Pinnacle Mountains that we could try; he wants to "stumble" across them by "accident," very probably at the last minute to avoid the whole Turn Undead thing mentioned above.
Essentially, I don't think he's looking for a cleric capable of casting Resurrection or other 7th level spells; as you say, Akura, he can do that himself. I think, rather that the operative question is: what kind of pilgrimage would call for so many powerful clerics to gather together at the same time in the rear end of nowhere, outside of dwarven lands? One that involves all of the North Gods except Hel? Are the vague situational similarities with another outcast Evil God we know about with a plot to blackmail the gods in order to ensure their own power and the protection of their followers, the Dark One, bugging anyone except me?
EDIT: Thought of another question. Why would Durkula need Roy and the Order of the Stick, instead of just heading off himself in the night? Also, and it might tie into that question, Durkula wants to get there ahead of the rush - he wants a fast ship to take him along the pilgrimage, and explicitly not to actually follow the pilgrims.
EDIT 2: ...he doesn't want the clerics at all. He wants to get to the pilgrimage site before them. Let's say you have some sort of powerful ritual you need to cast with a bunch of high-level casters in a particular location; what would happen if the place where you do it in was secretly contaminated or desecrated by a high-level but opposing caster before you ever got there?