Booting without a video card on a consumer grade board will be dodgy. Almost any server grade board will do it without blinking. This is basically because there needs to be some thought given in the BIOS programming to what to do if there's no video card. Your average server board will intercept the BIOS console traffic and redirect it to a serial port, or perhaps a virtual display that can be accessed via an IPMI subsystem. The consumer grade board isn't necessarily going to have all the instrumentation built into it to make that all work out. There are several levels at which this can go all wrong.
If you have an RS232 port on your board that's configured as COM1, you do have everything you need for a serial console. You do not need to have something *attached* to the serial console in order for it to be an operable serial console. If you do not attach a terminal of some sort, the system really has very little clue that there's nothing there, it's seeing no keystrokes and it can keep pumping serial data out. If you *do* attach a terminal, then of course you get to monitor and control your console from your terminal. Just like the old days.
If you wish to experiment, you may want to try something like sticking "-D -h" into "/boot.config". Or just "-h". This will push FreeBSD's console selection to serial as quickly in the boot process as possible through configuration alone. I don't know if FreeNAS will respect that. This is where it's *very* handy to pull out a laptop and hook up its serial port to your server, and actually find out what is going on, and where it is bombing. You might find that your system isn't actually hanging up where you think it is, or you might find some other obvious issue that can be fixed.
