Let me help you with this information.
It is important to say that if the motherboard has VGA output only the signal will be sent as VGA but if you have a DVI monitor you can use a cable VGA-DVI and it should work. As you mentioned, adapters are good option but we do not recommend them since the signal can be affected but you can try it.
If you connect a dedicated video card to your system the onboard graphics will be disabled and the video card will start working as main graphics controller but it is not necessary to this. Just using an adapter can help you fixing the issue.