While listening to Beethoven's 9th symphony 4th movement I noticed that "Elysium" sounds more like "Eliesium", and "Brüder" sounds similar to "Brieder" (example on Youtube). Moreover, even if we just look at the lyrics, we'll find that "wieder" is supposed to rhyme with "Brüder":
Deine Zauber binden wieder
Was die Mode streng geteilt;
Alle Menschen werden Brüder
Wo dein sanfter Flügel weilt.
So were these sounds so close to be almost indistinguishable at the beginning of XIX century? Are they still considered somehow interchangeable in pronunciation?