Yes, but you have to assume that the Congress critters are stumbling on some of the same evidence that Mueller is. I expected something juicy to leak by now, but thus far its been lots and lots and lots of smoke
Republicans control the congressional agenda. What they apparently want to discover is nothing & strive mightily to do so.
They are not privy to information gathered by our intelligence agencies in the same way as Mueller, either. I suspect the IC voluntarily submits information to Mueller that congress would have to request if they even knew to do so.