If the graphics adapter is on a enumerable bus such as PCI, bios or device tree have nothing to do with it. The Linux kernel PCI code will scan the bus and load the needed module.
Device tree/DMI are more useful in telling kernel about devices that cannot be automatically scanned. Usually such devices are "soldered on", so the need of changing the Device tree is quite rare.
Life in X86 and DMI is a bit more complicated, as Bios also probes some devices and puts them in DMI. Often instead of probing those devices in kernel again, we trust the bios with varying degrees of success.