I'm wondering if the "insectivorous bats" I remember from the Grzimek House in 2004 were actually Seba's. There were a whole group of them and I was surprised to see them - but I don't recall any identification on them, so they could have actually been Seba's. I just assumed they were insectivorous ones based on size.
@Chlidonias They certainly had Seba's back then, as they do now - according to ZTL, they have held the species since 1977 and in 2005 held 335.370.107
So I reckon you are correct.
(On another note, this year I shall hopefully be visiting Frankfurt myself; long beyond the days when it held anything like the treasures it once did, but I suspect I shall still enjoy it)