Is spam a part of the US?
For common usage among the public: No. Very generally here in the US, Spam kinda falls into its own utilitarian and cultural category. “Luncheon meat” by itself usually brings to mind cuts or products that are pre-sliced or else meant for thin slicing to use on sandwiches.
As lunch meat, it could be cooked or not. But for breakfast and dinner, it needs to be cooked. All spam is luncheon meat but not all luncheon meat is spam. Basic idea is that Spam is a type of luncheon meat. It’s also a brand name.