Hey, always good to see someone solve a system problem. Nice work!
Yes, definitely - any part of the graphics card can wreak havoc: chipset incompatibility, bad drivers, not enough memory, overheating, etc...
And, as you found out, it's smart to have an extra graphics card on hand for troubleshooting purposes (Especially since onboard graphics can be a mixed bag, sometimes on the cheap/low-end. Also, most modern graphics cards have two ports, allowing you to expand to two monitors if you wish).