You could point out to them that if we've been able to write a kernel that's good enough for them, we should be able to write drivers that are good enough as well.
As for patents, you could point out that whether their product has open source drivers or not has no bearing on whether it's infringing any patents. They can keep their drivers as close as they want and still be hit with patent lawsuits.
In the desktop and server space, there are many huge open source programs these days, programs that are essential in the enterprise market, and none of them have been hit with patent lawsuits any more than proprietary software of similar nature has been. I fail to understand the logic that assumes opening up code suddenly makes one more vulnerable to patent lawsuits.