At least two German zoos had mixed bear exhibits into the 1990s: Hannover and Osnabruck. I visited Osnabruck Zoo in 2002 and saw two Polar and two Brown in the exhibit. I went to Hannover Zoo two years later but the only resident left in the exhibit was an elderly female Brown Bear. As I heard the story, the zoos obtained many bear cubs of different species at the same time in the 1970s (Polar, Brown, Black, Asiatic Black and so on) and the plan was always to make different exhibits, but then I guess finance or other reasons prevented that. Even so, I have not heard of hybrids, but they may have been born.
I've checked my notes and there is no comment regarding bears being mixed at Hannover when I was there. However, at Artis I noted they had Sun Bears and Sloth Bears together.
