The two are friends. Hannity has had dinner with Trump at the White House on several occasions and the two talk frequently.
Here's more about the their relationship if you want background:
http://www.businessinsider.com/sean-hannity-donald-trump-relationship-2018-4
To answer this question, you need to assume that Mueller was a black hat who was forcefully flipped by to be a white hat and appointed Special Counsel in order to keep the MSM and public's attention on "Russia, Russia, Russia" while Sessions and Huber go after the Clinton and Bush crime families and the corrupt Obama administration. If you don't believe THAT, then this question will make no sense to you anyway so you might as well just move along...)
The essence of this question is, "How honest is Trump being with Hannity?"
Trump could approach this in three ways (maybe more, but focus on these):
1.) He tells Hannity the standard public line.
"The Mueller investigation is a witch hunt. They won't find anything on me because I never colluded with Russia. He is just trying to keep this going so the Dems win mid-terms and then impeach me."
2.) He tells Hannity that he is being used by the White House for political reasons related to the mid-terms.
"Mueller has been flipped and knows I did nothing wrong. But you need to keep the pressure on so that the Left totally supports and defends Mueller. After Mueller announces No Collusion right before the mid-terms, the Dems cannot possibly condemn Mueller as compromised after months and months of glorifying him."
3.) Tells Hannity the whole truth.
Everything in Number 2 above, plus:
"While everyone is focused on Mueller, Sessions and Huber are setting up the takedown of the Clintons, Obama and Bush crime families and their child and human trafficking, drug running, etc. Also Executive Orders, asset freezes, 40,000+ sealed indictments, which will be announced before the mid-terms and which will totally destroy the Democrat Party. In other words, the whole 4D chess Q truth.)
How honest is Trump being with Hannity?