FreeNAS 8.0.2 is based on FreeBSD 8.2, so if the 3114a is compatible with FreeBSD 8.2 (and I'm fairly sure it is) then there should be no problems with FreeNAS.
SiI3114 is old SATA 1.x chip without NCQ support. It is supported, but if you need card for PCI/PCI-X, I would recommend to look on SiI3124. It also has 4 channels, but it is much faster.