At Detroit's zoo, in the Outback section, there is a trail that you walk down right through where the Kangaroos are at. There are no fences that shield you from the animals or they from you. They can walk right across the trail in front of you if they wanted to. The person who was working there said that they for the most part don't come by the trail when people are walking, but there was one kangaroo there that had been rescued and was mainly raised by one of the workers there. She said that this kangaroo loves people and will come by the trail most of the time. I thought it was pretty interesting. So it can indeed be done.
I am not an expert on the animal, but there must be some reason that this is allowed for Kangaroos.
And also right here in Detroit in the middle of the summer, their zoo has an Artic Circle section, that has Polar Bears, seals, and penguins outside in the open. They are surrounded by iced surfaces and water, but just this summer I saw Polar Bear hanging out in the grass and not on the iced surfaces in 80 degree weather. So I don't think it would necessarily have to be all indoors, tho it might help!