The Ring-Tailed Lemurs used to be behind the fastpass area for It's Tough to be a bug, or since it doesn't have fastpass anymore I think, I believe they are near the main signage for It's tough to be a bug. Honestly I've been to AK a dozen times and I've never seen the collared lemurs though, nor have I seen a sign for them.
The otters are Asian Small Clawed Otters and were on the left hand side as you are walking towards Africa, on Discovery Island.
The Babirusa is one of the animals in the Oasis area, though sometimes those animals I have noticed aren't out if it's too cold especially early mornings.
Are there any animals that you specifically have to be in a line in order to see. I'd hope not, but I had heard examples that possibly you did.