Does anyone know if park hopper tickets purchased in Orlando can be used at Disney Anaheim?
no they can't
Here is what I read on mousesavers.com:
Interesting, unpublished fact: you can use leftover days on a Walt Disney World Hopper pass at Disneyland or DCA! This is probably because Disney World Hopper passes cost much more per day than Disneyland passes, so Disney is actually coming out way ahead on the deal. Present the Disney World Hopper at the gate on arrival -- they will take it somewhere, deduct a day from it, and give you a one-day Disneyland pass that allows you to visit both parks in the same day. This information was confirmed December 2004.
Disneyland passes are NOT accepted at Walt Disney World, and Annual Passes are only good at the park where they were purchased (WDW Annual Passes are NOT good at Disneyland, and vice versa)