The seeker cleric was a really interesting idea, but IMHO there are some serious problems with basing the sneak attacking man of God idea off the cleric chasis.
-9th level casting is an extremely good thing to have. Sneak stacking can also be pretty powerful. It's intently hard to make a balanced class that whacks things really hard and casts 9th level cleric spells.
-The whole idea of the class strongly implies a lot of skill ranks for things like hide/ms/open lock/traps/etc. but clerics have wet garbage for skill ranks per level. In their current state seekers may have to go many levels without taking rogue levels, meaning your ability to take ranks in fundamental skills like hide/ms is arbitrarily stunted for long periods. It feels a bit frustrating and inelegant.
-I think the concept would be better served in the form of a 4th or 6th level caster with more skill ranks, access to roguish skills and a more seemless leveling experience.