Yes, the All Saints' Eve dating of the disputationes was probably significant--Martin Luther was not without a flair for the dramatic nor a finely honed sense of how to twist the knife once he'd inserted it. But to understand why he picked this date means looking at how the "95 theses," as we call them, were unleashed.

It's possible Luther posted them on church doors of Wittenberg. This would not have been particularly unusual; they served as bulletin boards for announcements. In particular, for annoucements of university events like disputations (formal debates using scholastic methodology) to be held in public. Luther's theses ostensibly took the form of propositions to be debated as such, hence his original Latin label them as "my disputations." Taken as a whole, however, the text doesn't really lend itself to the format of propositions for an actual debate: the "theses" are more like bullet points or steps in an argument, with several points leading to a conclusion leading to the next conclusion.

The story that Luther posted the theses in public in Wittenberg is told by others, and later--scholars have devoted enormous effort to getting as close as possible to the event, but the best we can do is within a few years. But as several of Luther's biographers have pointed out, unleashing the theses in Wittenberg was kind of a dead end as far as wider polemical purpose went. They were in Latin initially, so only legible to the elite, and Wittenberg was neither exactly the leading university of Europe nor a hotbed of lay (non-university) Latinate humanism. So whether or not the so-called "Thesenanschlag" occurred as legend has it, is more relevant for the mythmaking of Luther as iconoclastic hero from the beginning (in contrast to his initial stance of reforming the existing Roman Church, not Reforming).

Instead, we can look at how Luther actually first publicized his theses: via letter, to the archbishop of Mainz (in whose archdioceses Wittenberg lay). Letters in the late Middle Ages/early modern era weren't just bits of communication from one person to another; they served as vehicles for texts of all sorts, including sermons and treatises, with the added bonus of the "letter" part perhaps supplying some context (recipient, date) towards legitimizing the contents. That is, they were public documents--hoped, assumed, or at least grudgingly accepting the possibility of being publicized at some point.

So when Luther sent his disputationes to Albrecht on 31 October, the eve of All Saints', that date would be attached to the document for the learned, especially ecclesiastic (because Latinate) readers in Albrecht's household and beyond. Now, keep in mind that Luther's original opposition was not to the cult of the saints as such; in fact, Luther's own theological development shows he was perfectly fine with preserving saints' cultus fairly far into the 1520s, and adapted his views more or less in response to trying to tame the wilder/more radical reactions of evangelical enthusiasts.

But All Saints' Day, in electoral Saxony, wasn't just yet another day to honor saints. Rather, amidst the rich liturgical calendar of the late medieval Church, it was the day that the insanely large relic collection of Saxon prince-elector Frederick the Wise went on display--with lavish promises of indulgences for pilgrims who went to view it. Archbishop Albrecht, the letter's/theses' initial recipient, would have known this; the scribes in his secretariat would have known this; the initial discussants of the theses would have known this. And, of course, when the letter mysteriously leaked to the public--first in Latin, but quickly in vernacular German as well--the monastic, ecclesiastic, and university communities of Wittenberg would have recognized this.

And, Luther clearly hoped, would have been taken aback by the audacity of his proposition: funding for the university was heavily abetted by proceeds from the relic-show pilgrimage. Doctor Luther's willing attack on the source of monetary life for his own university, the professor evidently hoped, would help convince his elite, Latinate, local audience just how severe the state of indulgence abuse in the Church had become.

It's not always wrong to accuse Luther of being a bit of a drama mama, but in this case--yes, he was making a point.