hey Will,
from a not-so-purist perspective, i think that Satanic evils "infecting and/or influencing humanity" is extremely Lovecraftian.
for instance, try and count how many references to demons, demoniacal, satanic, hell, satan, infernal, etc. there are in his works. i'd say over 100. for a handful of short mythos stories, that is pretty darned obsessive.
however, a word like satanic means different things to different people. i'd agree that Lovecraft might have been trying to put unknowable, alien forces into a perspective that humans could understand: evil personified by the creatures of darkness that oppose god and christianity. one can only go on about how beings are ineffable, unknowable, and indescribable so long before they leave absolutely no impression on the reader at all. hence the forced cultural take on the above adjectives.
of course, it's just my opinion and i'm very biased since i happen to be a Lovecraft lover and a Satanist.
Darrick
http://www.CultofCthulhu.net