There actually is a way to get deinterlaced video from a capture card with OBS, and in 60 FPS no less! Here's what you can do:
1. Download AmarecTV 2.20c from this link:
http://cgi.geocities.jp/amarectv/cgi-bi ... tv220c.zip
2. In Amarec's config: Graph 1 settings should be pretty self-explanatory aside from a couple things; set the capture card's audio input to (Link), and use Master Volume for your audio capture device's volume. Under Graph 2 (Preview), set Deinterlacing to "Auto select", Function to
anything except "HW Deinterlacing" (Retro Game is obv best for 8/16-bit stuff), and Scan Line Doubler to "Auto". I would also recommend using a custom aspect ratio of 3:2 if you're using a 720x480 capture card (which Dazzle and EasyCap both are). Under the Live graph, check the box to enable Live and set FPS to 30 (or 60 if you desire). The Live resolution should also match your capture card's, and the audio quality should match that of all other programs involved in your stream.
3. In OBS, add a video capture device and select Amarec Video Capture (Amarec must be open to use this, btw). Set its size/position in your stream, and you should be good to go! Earlier versions of Amarec cannot stream or record legitimate 60 FPS, so I linked 2.20c just in case anyone might be interested in trying that.
If this helps anyone, give your thanks to Omnigamer! He's the one who figured all this out. And obviously deinterlacing options in OBS would be nice, but I figured this was still worth posting. =)