As long as the major specs match up, i.e. DDR2, SO-DIMM 200 pin and 1.8V, then it should work. You can have mismatches in the minor specs like the frequency and timing. The memory controller will just use the slower module's timing in order to use both memory modules.

Those twin pack matched memory are optimized for dual channel operations, but not required. Today's memory controllers can support asymmetric dual channel mode so you can gain some of the dual channel mode speed boost even with differently sized modules.

Crucial and Kingston used to have different part numbers for each system, even though they ship you a common module that can be used on different systems. It was one of the requirements for their compatibility guarantee.