I work with gallium-indium-tin eutectic metals routinely. They definitely do not play well with some metals, specifically those commonly used in heat sinks. It will readily react with both aluminum and copper resulting in a nasty grayish black compound...not so good for moving heat.
However, I do use it against nickel plated copper surfaces with no problems provided that the nickel strike is well done; i.e. it's not porous. The metals it does play well with are typically stainless steel, but stainless is a very bad conductor of heat relative to copper and aluminum.