The best test you can do to see if the card will mine would be to go to
www.bitminter.com and create an account.
You can use the software that is supplied by the pool, its the easiest start anyone could find.
Even though it will only mine bitcoins, it is a good test for your rig.
You dont need to be getting a display from a video card to be able to mine with it.
I have a PC video card in my Mac Pro that mines for me, and it has never been attached to a monitor, the other video card in my Mac does that for me.
You should be able to use only the motherboard video with no problems.
Dont forget you will still need to load the drivers for the other video cards though.
edit:
Is your power supply up to the job? You need about 200 watts per card and at least 200 watts for the motherboard.
Just work with one card at a time, add another when you have the simpler setup running.