I found this dramatic reading of Akutagawa Ryunosuke's 羅生門, in which the performer reads 誰 consistently as たれ.
Is this correct for the time period? I know that 誰 has old readings resembling た/たれ such as 誰がために鐘はなる, but when did readings beginning in t- cease to become current?
日本国語大辞典 says:
近世「だれ」と変化したが、「随筆・松屋筆記‐五五・三」「徒然慰草‐一・二二段」に「今云あの人たちのもの申さるることばをきくに或は『たれ』といふことを『た』の字をにごり〈略〉かやうのかたこといくらといふかずをしらず丸か耳にさへをかしく伝ればこれをいにしへの人たちにきかせ奉らばいかばかりかなしくおぼしめされん」とあり、近世後期からの現象と思われる。現代では、「だれ」が一般的であるが、主に文語脈の中では、「たれ」ともいう。
Judging from 松屋筆記 is written in 1818-1845, and 徒然慰草 is some point before 1650, the current pronunciation gradually replaced it during the Edo period. 誰 is etymologically from voiceless た, but assumably changed into だれ by analogy to ど-series question words.
Is this correct for the time period?
Well, it's "correct" for the story's background which seems to be late 12th century, but considering that the story is written consistently in today's Japanese, I'm not sure if it's faithful to the author's intention. As I noted in my comment, I couldn't find other recitation saying たれ on YouTube.
It's not what you'd expect for colloquial speech in the early 20th C., but it's believable as an Akutagawan quirk. (Maybe affected, maybe not.) He was obviously familiar with a huge range of older narrative styles and material (Rashomon is basically an elaboration on a Konjaku Monogatarishu story), and there is evidence of him using the reading elsewhere without any obvious reason.
So I wouldn't expect a regular modern narrator to use "tare" reading the story aloud, but maybe a superfan more familiar with Akutagawa's entire body of work would do so intentionally based on what they knew.
According to スーパー大辞林 published by Sanseido, “誰” was pronounced “たれ" in old time and started to be pronounced as “だれ” in “近世 ‐ the later part of feudalistic era ie, Azuchi, Momoyama and Edo era (1573 – 1895).
The early pronunciation of “誰" as “たれ” is notably found in the phrase, “わかよたれそつねならむ - 我が世誰ぞ常ならむ – What can be permanent in this transient world?” in the いろは歌, which was believed to be created by the great Buddhist priest, 空海 (AD 774 -835), but actually created later than that.
