I wouldn't recommend any other mbuna, but yellow labs are so calm that it could possibly work. Obviously you are taking a risk, because the fronts could eat the yellow labs at any time, if they chose to do so. You have the best chance if you introduce small fronts to adult yellow labs, and I'd say you have virtually no chance if you put yellow lab fry in a tank with adult fronts. Anything in between is hit and miss, but it could work - at least for some time.
Regarding the leleupi, I am keeping them with my fronts in a 240G, and the mix has worked well now for about 6 years. In a 6' tank like a 180G I would probably try the yellow labs rather than the leleupi. A breeding pair of leleupi can get fairly aggressive, and defend a rather large territory, which would take valuable real estate away from your fronts. Yellow labs generally don't defend a territory in that way.