I don't think they did....Kimba has alot of similarities with TLK, but thats because it 1.) took place in the same environment, 2.) it was a full animated series wasn't it? That means it had a lot more scenes than any movie would ever have. I mean theres probably a good chance that one scene in the hundreds of thousands of Kimba scenes would match a scene in TLK.
If Disney really copied Kimba. Then I know why Disney changed the name from Kimba to Simba. Its really funny & surprising. Check it out yourself and find out what Kimba really means in Swahili. http://africanlanguages.com/swahili/