Yes, but when you have two sets of different HDDs, two arrays would benefit the speed of each array.
For example:
SET 1 - 4 HDDs of old drives @ 150 MB/s - 1 Parity, 3 Data - For Surveilance System (Drives allways spinning 24x7x365)
SET 1 - 5 HDDs of Newest drives @ 280 MB/s - 1 Parity, 4 Data - For General Data (Only spins whenever needed)
I think in this scenario, two arrays would be a great value.