Did Martin Luther nail them up on October 31st of the Gregorian or of the Julian calendar? My guess based on other things I have been reading (including on this subreddit, but I want to be absolutely certain) is that it was the Julian Calendar, in which case it really happened November 10th by the Gregorian Calendar. Can someone set me straight on this? I'm writing something on my blog about it.
The change had not yet occurred. Typically, when we are talking about dates before the switch we don't correct for the later change. So yes, today would be the day that we can commemorate the 95 theses. To put it another way you can speak of Julian dates after 1582 (not everyone adopted right away) but you can't speak of Gregorian dates before 1582 (even though you can technically calculate them).