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.
A Lion install removes the driver for the Tempo SATA E2P, Tempo SATA ExpressCard/34, and Tempo SATA edge ExpressCard/34. Just reinstall the driver and the card will work again.