I have just researched Minhag Teiman a bit - and while
I did not get all the details - I did finally just confirm with a Teimani Talmid Hacham: that Teimanim do indeed observe a form of Aveilut during Sefirah
He also mentioned their minhag to count Sefirah using Aramaic
This means re: Aveilut in Sefirah that it is even more widely "nispasheit" than EG the restrictions of Meat and Wine during Hodesh Av, when Teimanim only restrict themselves on Erev Tisha b'av after Hatzot.
A few comments:
A. Both The Teimani and the S'phardic practices seem to be unrelated to the Crusades
B. While The Narrative from the Talmud re: Talmidei R Akiva probably did not trigger this Minhag immediately, nevertheless it HAS seem to have taken hold in East-West Ashk'naz, S'pharad and Teiman, albeit the severity may differ as well as the specific days selected
C. My hypothesis* about Hol Hamoed might explain some of this widespread observance [But it also might not! LOL].
* That is the Minhag to refrain from Nissuin and Tisporet and some m'lachah was originally triggered by Hol haMoed first, and later morphed to Aveilut - probably due to the Crusades.