Can culter hammer breakers be used in a GE panel or must GE breakers be installed? I was told installing CH breakers in a GE panel is against code?

Check the instructions or datasheet for the CH breaker. Most likely not able to use in GE panels due to UL Listing. There are a few breakers that are UL Listed to work in other panels.

Cutler-Hammer does have breakers that are UL certified to fit 6 other manufacturer's panels. GE is one of them. The only way to know if you can use a different manufacturer's breaker is to do the research.

The person that told you installing a CH breaker in a GE panel was against code made a general statement that is false. Here is a link to the CH classified replacement breaker information page if he doesn't believe you. Link (http://www.eaton.com/EatonCom/Markets/Electrical/Products/ResidentialProducts/CircuitBreakers/ClassifiedReplacementCircuitBreakers/index.htm?ssSourceNodeId=3483&ssSourceSiteId=EatonCom)

Keep in mind, only the Cutler Hammer Type CL and CHQ are listed as replacement breakers allowed in other panels.

Not the standard and popular Type BR or CH.