I have a Geforce GTX 570 with 1GB of dedicated RAM currently. If I bought a video card that goes into a PCI-e slot or something of the like, could I plug monitors into it and use it's VRAM without SLI?
Any monitors hooked up to the 570 will use that gpu's vram. Any monitor hooked up to the other gpu will use its vram. Actual vram usage gets a bit complicated as things can be duplicated or just use the other gpu as a passthrough.
Sli does not add vram, everything gets duplicates on all cards. This means non sli will have more vram. But then with no sli, only the primary gpu gets used in games.