I think you are thinking a bit too about it. It's as Scottish as 'bloody' Brigadoon. I don't think there is even that much thought given to the war, it's a backdrop rather than the foreground as in Colonel Blimp. It's simply to me a classic tale of opposites, or those who appear opposite set against a mythical take on humanity.
Livesey in the Powell and Pressberger films just seems like a muse of decency and in that sense is representative of a quintessence of what we would at least argue was being fought for, but given the role of Anton Walbrook on Blimp, I think the Archers were trying for a universalism.
I am not sure what you are getting at in terms of the SNP, but there is a strain in the film that could be argued for strong devolution and location bring central. 'the fish, they.do may know him'.
But since I am not a supporter of independence for reasons like that, it is unimportant (leaving aside that I don't really think it is about Scotland anymore than Outlander is)