I take it from your email you figured this out, but:
Audio from a capture device that comes into OBS isn't audible anywhere unless you turn on monitoring. You need to turn on monitoring for each source you need to listen to in Edit > Advanced Audio Properties, and then you need to pick one Windows audio device to use to listen to those monitored devices in Settings > Audio > Advanced > Monitoring Device.
A lot of users are either 1) using external capture hardware or cameras, or 2) capturing audio and video from a local application like a game. Not everyone is doing both, but if you are, you need to be careful what you set your Monitoring Device to, because if that is your system default audio, and you're capturing that, because you're capturing a local application, you will get an echo.
If you end up needing more precise control over Windows audio routing, but don't want to use a full-blown DAW, a good choice is Voicemeeter, which is free, and there are guides for using it with OBS:
With the Software Voicemeeter Banana by the guys from VB-Audio Software you can manage several Audio In and Outputs to give you the options to decide which sound should go onto your stream or recording and which goes to your speakers, headset or...
obsproject.com
If you don't need do VO, then you don't need a microphone, just disable it. If the UTAP video capture is set to "capture only" and the only audio you need is the embedded audio in your SDI feed, then you can leave all other audio devices in Settings > Audio disabled.
OBS works fine with Win10 as long as you're at least at patch level 1803.