Yes, this is a great way to expand capacity and performance. If two or more Tempo-X, X4+4, X8, X4i, X4P, E4i, or E4P cards are installed to the same machine they must all have the same firmware version to avoid conflicts.
Tempo SATA X4P and Mac OS X 10.4 requires the final version, 10.4.11 for tested functionality. For example, a RAID 1 set does not function under Mac OS X 10.4.6 in a Power Mac G4 Quicksilver.