See my edit above for some more clarification.Interesting. I'm extremely dubious of this but admit I have no standing to question this. Irrespectively, it's entirely unclear if that provides halachik justification to make a bracha.
I do not think anyone outside of Lubavitch is capable of understanding this.
Honestly, it's not that difficult to understand that the same people who will go to the ends of the earth, literally, to get one single Jew to make one single brachah, one single time, and not give it a second thought, wouldn't be more bothered by rain than by missing a brachah.
It's not that we're any more "yechidei segulah" than anyone else, it's that the Rebbe lit a fire under us, and taught us the value of a mitzvah, no matter what. Even if, to borrow an example, you spend hoshana raba at a ballgame.
I am spending Yom Tov in a city with barely a minyan of shomer shabbos families. One of the Orthodox community members arranged a sukkah hop on Thursday night going from sukkah to sukkah at every Jewish orginzation, including Temples, etc. The last stop was at Chabad, and he told everyone that Chabad was last on the map, but it was the most important one. Because without Chabad there would be no sukkah hop. He explained:
About 20 years ago, he knew virtually nothing about yiddishkeit other than the fact he was Jewish himself. He met a Shliach who naturally encouraged him to do mitzvos, but one of the first occasions he was at the Chabad House was sukkos. The rain was pouring. The shliach was drenched, but eating in the sukkah. He assured this man he could eat inside and he need not eat in the sukkah. "But then why are you eating in the sukkah in the rain?" he asked the Shliach? "When I have the chance to connect with G-d and sit in His presence, rain isn't going to bother me." The man thought about it and joined the Shliach in the sukkah. He was not shomer shabbos, he didn't know what those words meant. Had you served him treif, he would have eaten it in the Shliach's sukkah, as he wouldn't have known it was a problem. But at that moment, he would have only eaten that tarfus in a sukkah!
I know the Shliach he was talking about. I'm telling you there are numerous obvious reasons he would not be considered "meyuchad" in any way. But he learned from the Rebbe not only the value of the mitzvah, but he was tofeach al mnas lhatfiach and passed it on to another Yid.
Years later, many Chabad Houses later, that man now is mostly shomer Torah umitzvos, raising a family of Jewish kids who are learning and doing more than him, and is arranging events to get other Yidden to do the same.
This is one story that happened to one single person that I just happened to hear a couple days ago.
I'm far from the most "farbrente Chassidim", too borrow yet another term. Yet I've walked miles in the rain on tahalucha just to spread simchas Yom Tov and dance in a shul on simchas Torah, or to blow shofar for a couple of people, or even just danced in the rain on the street for simchas Beis hashoevah. I'm not more holy than anyone on this thread. But when the Rebbe inculcates the value of positive actions and mitzvos, he turned each of us into anshei maaseh, even if we aren't yechidei segulah.