Can I use a capture card with WebCamTexture

I see that there is a rather expensive plugin for Capture Card support:

http://www.renderheads.com/portfolio/UnityAVProLiveCamera/content.php

but also that there is some talk about using capture cards with WebCamTexture:

http://forum.unity3d.com/threads/116877-WebCamTexture-with-Decklink-SDI

I want to purchase a USB 3.0 capture card capable of taking RCA video and displaying it on a texture in Unity Pro, but I want to know if I need to purchase this plugin, or if it's possible to use it as a WebCamTexture.

Bonus points if anyone can recommend such an adapter.

Thanks!