black lancers can be tough to keep with others as they are very nocturnal, in my limited experience and from what I've heard. the lima should grow a lot faster than the lancer, so watch out for that. if the lancer is too big to fit in the limas mouth and there are plenty of hiding places for the lancer, i don't think you would have a problem.
however, I have a 10"+ LSN and a 5" black lancer and I will never try them in the same tank. IMO, the lancer should be full grown or at least a lot larger than the LSN (not large enough to eat it though)