I have the exact same card in my system and it works very well. However, I've never tried to boot from it. My (mirrored) SSD boot drives are attached directly to the SATA ports on my MB.
Can you tell us more about your boot medium? What version of FreeNAS are you trying to use? How did you create the boot medium? Since your screen shot shows 8 WD 4TB drives I can but assume you use those as your pool, so where and what is (are) your boot drive(s) and how are they connected to the machine? Please provide full hardware details as per the forum rules.