Mixing different types of SSDs in RAID volumes is a rather unknown area in PCs, I've never seen anything written about it.
I can tell you that when combining SSDs of different capacities in RAID volumes, the capacity of the resulting volume is determined by the smallest capacity SSD used. For example, a RAID 0 volume composed of a 60GB and 120GB SSD, will only have a total capacity of 120GB.
Matching the SSD controllers could be important, given the behavior I have seen with different SSD controllers. If the 530 SSD uses the SandForce 2281 controller, and only differs in the type of NAND from the 520, then it may work together fine. Whether or not the SSD's firmware makes a difference is another question.