If you're talking 2 different modules of 'compatible' memory - then yes it should work fine.
If you're comparing geniune to generic (IE: DELL to Crucial) then be careful.
I know of many models of proprietry systems (Mainly among certain HP machines) that wont take non-genuine memory, because of an identifying tag in the 'firmware' (not really, but still) of the module. Also non-standard latencies are common in proprietry machines to stop the use of non-genuine memory.
I dont know if Crucial goto the lengths of testing that Kingston do, but you're always safe with the Kingston equivalent of a manufacturer's genuine RAM.
Hope this helps...