Protector, welcome aboard.
I think most of us here are always glad to see musicians who are willing to come down from the clouds and discuss their music and beliefs, regardless of whether they fall in line with what many of us believe.
We could spend all year arguing about the provenance of the various instruments or the exact ethnic lineage of the blues and get no closer to the truth. Scholars have kicked these questions back and forth for decades, but no one really has an answer that is satisfactory: too much has simply been lost in the mists of time.
In any event, the reality is that, whatever the origins of the guitar and other instruments may be, they have been central to European musical culture for centuries, so the use of guitar hardly calls into question the 'Europeaness' (for lack of a better word) of metal. The blues seem even less relevant, because, in my view, metal emerged as a form distinct from rock precisely because metal moved away from the blues tradition - away from blues-based tonality; away from blues-based structures; away from the party hearty hedonism rock had inherited from the blues (which isn't to say that metalheads don't party, just that hedonism is subordinated to and sublimated within a Will-to-Power warrior ethos that is clearly modelled on a form of European martial idealism). Instead, metal increasingly adopted the ideals and techniques of the European classical tradition, making epic, structuralist music celebrating a martial idealism that is peculiarly European.
Now, I've certainly never been privy to the inner workings of your creative process, but I have to admit that when I listen to Summoning what I hear (and I have a fairly vast lexicon of musical history to draw on) is a thousand years of Germanic musical culture condensed (if that word can be fairly applied to a band famed for albums consisting of 10+ minute epics) into a new musical mythology celebrating a world that has passed and looking to a world that could be again. You might just as well try to hold back the wind as try to demand that 'nazis' not like your music. And, let's be honest, nobody but an idiot is going to assume that Summoning is a National Socialist outfit because they saw a video on YouTube. Do you really care all that much what morons think?
Just as a curiosity, who would you say your primary influences are? I hear Burzum, mid-period Bathory, Wagner, medieval/Renaissance polyphony and, on occasion, darkwave or maybe even Dead Can Dance, but it's always possible that what I'm hearing is parallel evolution.