Doing more research into the matter with the latest 0.651b, same issue with x264, but it only happens when I'm recording w/ my Twitch profile in OBS. I'm assuming this is bc it's outputting FLV.
I can't import FLV into Sony Vegas, and I'm assuming just the .mp4 extension allows Vegas to import the MP4 file, but it's still an FLV in disguise which is why there's nothing there. So the real question here has nothing to do w/ OBS which is who to convert an FLV to MP4 right?
[EDIT]: More news, found out using
HandBreak to convert it to MP4 through the H.264 (x264) video codec got it working. Now, this is double-compression, but if you set it to Constant Quality RF14, you should be fine. Please correct me if I'm wrong. This will increase your filesize, but will give you something to work with in Vegas.
One quirk, you'll need to set the audio to the AAC passthru instead of auto passthru (even if you recorded using MP3), or it won't work.