It depends on the type, model, made of the processor. Some of Intel Mobile processors (laptop processors) are embedded, some are not. Upgradeable or not depend on many factors, such as processor, motherboard/logic board, etc.
Based on my knowledge, embedded means soldered/attached on the motherboard/logic board and cannot be removed. Because of the limited space available on some laptop computers, some manufacturers have to choose this kind of processor.
I suggest this link for more info.: http://ark.intel.com/ProductCollection.a...
You may find more information about those two types of processors and probably more information about the ECC memory. For some reasons, it doesn't matter if the processor supports ECC memory, the Apple laptop computer may or may not support that feature if the Apple doesn't want the laptop to support such feature, just like what they do with the 64-bit processing/kernel on most Apple laptop computers.
Hope this helps answering your questions.