Can the boot drive select screen be used with a PC video card? Since installing an unsupported video card typically means you don't get a boot screen on OS X, does that also preclude selecting boot drives on startup by holding down the option key?

I'm looking at getting a Radeon 6870 for a MacPro3,1 for use on OS X Lion. I've filled all the drive bays and sometimes have different OSs installed. I'd also like to know if I'm going to loose access to the recovery drive if I happen to need it.

If unsupported cards do prevent the boot drive selection screen from displaying, could I install a second 'supported' card in one of the PCIe x4 slots (the other x16 will be blocked) and get the boot drive selection screen back (by plugging in a monitor to it when necessary)?

What there any other deficiencies I can expect with this setup? Is a card that works but is unsupported on Lion likely to stop working with future versions of OS X (e.g., Mountain Lion).
The card works fine in Lion but, indeed, without a boot screen or boot drive selection. I've left an old supported video card in another slot, and hooking a monitor to that card shows the boot screen/boot drive selection screen.

I haven't had a chance to try out Mountain Lion on it.