It's an interesting one, isn't it?
I'm wondering if the phase in which something is summoned affects its rules. My inclination right now is to say that specific effects over-rule general rules like summoning restrictions, so Greyseer is okay, but in the case of the dial advance summon, because (as you say) it doesn't say "anywhere" you're limited to normal placement rules.
Also of interest, and related, is whether moving a bunch of Skaven in the corruption phase (via their upgrade moving them on ruination, or via Skitterleap moving them on domination) trigger / interact with "if opponent summons a figure to this region" effects.
I'm thinking specifically Field of Ecstacy, and two cards I can't remember the name of: the Nurgle one that gives VP for each summon, and the Tzeentch one that charges extra power for the summon, and the Khorne card Hate.
The Field of Ecstacy seems straightforward - Slaanesh gains a pile of Power but can't spend it because its not the summoning phase.
The Nurgle one seems straightforward too - Nurgle gains a load of VP.
Hate, I would say, would prevent Skitterleaping, as it prevents being summoned away, and movement is summoning.
The Tzeentch one is trickier - would the Skaven player really have to keep Power spare to be able to Skitterleap into that region?
Part of me wishes that FFG had said that only "summon" counts as summoning, and had move and place mean what they sound like - moving and placing figures without summoning.