FOX does promote the UFC, only for big cards though. I'm pretty sure I've seen 2-3 cards mention on there before. I didn't see a single mention of this FOX card though, maybe because it didn't have any huge names. Silva isn't exactly known to most casuals who watch NFL.
I don't think this FOX does is turning out as big as many people thought when it was first announced. Is the UFC more successful by partnering with FOX? I don't think so. Outside of that big paycheck they get each year from that contract, I don't think FOX adds any new fans with the limited marketing.
FOX could definitely make a better effort to mention everything going on with the UFC, but I can see why they don't.