Pathfinder: prestige class and base class caster level

[Scottlang]

I have a player who is playing a witch, and is thinking of taking levels in a prestige class (Feysworn) and asks, does the prestige class also stack with the caster level of the witch for determining the DC of the witches hex?? And other abilities...
He says: the rules say, that the caster level = class level and both of those are equal to the level of the witch...??
Does this mean the DC of the hex's??

[Daefos]

I have a player who is playing a witch, and is thinking of taking levels in a prestige class (Feysworn) and asks, does the prestige class also stack with the caster level of the witch for determining the DC of the witches hex?? And other abilities...
He says: the rules say, that the caster level = class level and both of those are equal to the level of the witch...??
Does this mean the DC of the hex's??

No. The DC to resist a Witch's Hex is 10 + half your Witch level + your Intelligence modifier; your caster level has nothing to do with your Hex DCs. Unless the Feysworn explicitly mentions that it stacks with Witch levels to determine the DC of Hexes (and I don't see any such language in the class write-up), then the default assumption is that they don't.

[Psyren]

You also won't get new Hexes unless the PrC advances the Hex class feature, which this one doesn't. (I haven't been through all of the Eldest boons though)