Rebbi Yishmael is indeed a Tana and is quoted by Rebbi Yochanan on many occasions. See, for example, Sotah 26b, Zevachim 86a. However, note the language, "Mishum Rebbi Yishmael" -- lit. "in the name of Rebbi Yishmael," as Rebbi Yochanan did not hear it directly from Rebbi Yishmael; there was a gap of some 140 years between them. Rather, he heard it in the name of Rebbi Yishmael. Many Amora'im quote Tana'im, and Rebbi Yochanan frequently quotes his teacher Rebbi Shimon ben Yehotzadak as well as Tana'im he could not have known personally (Rebbi Yosi, Rebbi Meir, Rebbi Eliezer ben Yakov, and Raban Shimon bar Yochai). (A number of the quotes from Raban Shimon bar Yochai should actually be ascribed to Rebbi Shimon ben Yehotzadak, who had the same initials.)

Yoel Domb