There are differing opinions when it comes to mixing brands of DDR memory. Some experts say it should cause no problems while others say it can cause unexpected problems. At the theoretical level, mixing brands should not be a problem. All DDR memory comes from the same protocols. The idea was to standardize memory in most computers. This allows for upgrades and other changes without having to replace an entire computer or its motherboard. Standardization of protocols does not rule out specific manufacturer peculiarities.
In reality, mixing brands of DDR memory can cause problems in some situations. While each manufacturer is supposed to use the same standards, each one has their own spin on the DDR memory protocols. These minor differences can cause operational problems when you start mixing different brands. On the theoretical level, it is possible. However, minor memory problems can cause issues with power usage, responsiveness, and CPU cycling. It can also cause problem with memory retention during program operations or at shutdown or startup. All of these problems may be resolved by using the same brand of DDR memory in all slots on the motherboard.