To see decryption I would guess you need to be in the same hex on Gobwin Knob's turn. And while a barbarian warlord theoretically could hang around in the hex while Wanda decrypts (because warlord led stacks does not have to atack each other) I think Wanda would attack and then decrypt them too.
To see what individual units does in another hex I think would require lookomancy.
Parson's can't see the hex boundary without his funky glasses, Maggie says she "gain a clearer view of the area within the new hex." So they can see the next hex it is just a little hazy.