I know that Judaism doesn't allow for marriage between two men. Apparently, there's an exception for those who lead the services in the synagogue. (In a number of very traditional synagogues, I've heard people refer to the "husband of the kore [=Torah reader]" and the "husband of the tokea [=shofar blower]".)
What is the source and/or reason for this exemption?
I believe the basis for the exception for leaders comes from Devarim 15:2, which refers to בעל משה, Moses' husband. If the first leader of the Jewish people had a husband, surely future leaders are no worse. Leaders of services took the practice from there.
Strict halacha forbids this indeed but there must be kabbalistic reasons allowing it because some of the biggest Hassidic rabbanim were the husband of the Good Name and the husband of the Tanya.
Who said the exception was only for prayer leaders? Isaiah 40:4 says:
כל גיא ינשא -- every gay will marry
Very simple.(1) The reader and tokeah were women.
Although certainly questionable from a halakhic perspective, it appears that these communities must assume something along the following lines:
Husband of the Kore
The Talmud states that really women could receive aliyot, but the rabbis said that women should not receive aliyot because of the dignity of the congregation. Either this concern no longer applies, or it does, but is superseded by larger concerns of women not feeling that their Jewish ritual life is meaningful.
Husband of the Tokea
This is more problematic (cf. Rosh HaShana 29a), and the question of why they had a women blowing the shofar is even more pronounced (and should perhaps be asked separately). The likeliest explanation, is that they were referring to (the husband of) the woman who was blowing for herself (cf. Mahzor Vitry 316). Note especially Maggid Mishneh to Hilkhot Shofar (2:2) who writes that the custom is for women to blow the shofar and make a blessing on this.
Although technically their husbands would be the בעל קוראת and בעל תוקעת respectively, these sorts of grammatical mistakes are quite common (see e.g. Mishnah Berurah 8:14), especially with such unfamiliar words.
(1) à la the doctor is his mother.
It is a pshat for the husbands of the batim. But the husbands of the Mikra, the husbands of the Mishna and the husbands of the Talmud says "H' malach, Gay out lavesh"[1].
You don't need to be married to be a "husband" the original workaholics where the farmers שדה בעל and wagon drivers בעל העגלה. Husband is just a borrowed term of someone or something you are attached to but not necessarily by the bounds of matrimony.
While you have asked an excellent and bvery important question, I'm surprised that you didn't mention, perhaps, the most important husband, the Ba'al tefilah. So, with your permission, I'll explain why the need for this role.
Years ago, chazzanim were more common. They learned the art of nusach and singing in shul, and each Shabbat and Yom Tov, they gave a musical "performance". Yes, many of them croaked or yodeled and the services were long and ended on Shabbat about noon or so.
Have you heard most of the guys who pray, now? They have poor voices, don't know the nusach well, and basically, just sing Carlebach tunes and mumble or rush through the davening so that everyone can get to the chulent before it gets cold and hard.
So any shul that uses just any non-professional davener to lead the service needs a husband to tell the prayer leader how to sing properly, pace himself properly, etc. What's interesting is that this husband is also polygamous and is a husband to more than one prayer leader! (I won't delve into the legality of this, but, essentially, an exemption is made for religious reasons.)
Those shuls that still use a professional chazzan, don't need a husband, because these guys know what they're doing.
As a Torah reader myself, for many years, I can tell you why they call me the husband of the reader, in my shul, at least. The "reader", in this case is the gabbai. In many cases, one or both of the gabba'im incorrectly "correct" me. I.e., they tell me something I said was wrong, when, in fact, it was correct. In one case, the gabbai was looking at the wrong verse! So, as a husband, I have to politely remind him to clean his glasses, and keep on track. Granted, this situation may be somewhat unique to my shul, though. Shul politics dictate whom they choose for gabba'im in my shul, despite my occasional complaints to the rabbi.
