Interesting choice... you don't think there's too much bad blood between Trump and Cruz? You make a good point here - hatchet men can help...
Bad blood is relative. Remember early on in their campaigns they both went out of their ways to not attack each other.
Then, when Cruz abruptly dropped out, it sealed the nomination for Trump, which might suggest that Trump offered Cruz an incentive. Big business can often be this way, with personalities set aside for “the deal”.
Personally, about the optimum scenario for me would be for Trump to use Cruz to slash and burn the government, which since it would ruin him politically, then to make a deal with Mitch McConnell to shepherd him through the senate in a nomination for the SCOTUS.
This would mean ruination for both bloated parts of the government and the Democrats. That is why Trump floated the list of nominees for Scalia’s seat. To put in a strong conservative justice, but one who can get through the senate; then after Cruz does his job as VP, he gets the next seat, like that of Ginsburg.