For the segment involving an ambulance as well as Braun Strowman, WWE hired a local company that uses actors and a fake fire truck. In the ambulance segment where they pried open the door and got Braun Strowman out at Great Balls of Fire, the truck was rented and the people involved were hired actors.
In regards to Great Balls of Fire, Vince McMahon made two late changes to the finishes of a couple of Great Balls of Fire matches. First, Bray Wyatt beating Seth Rollins was changed the day before the show, possibly because WWE is getting ready to strengthen the heel side in the event Roman Reigns is given the Universal title at SummerSlam.
When that match had its finish changed, it was a massively heel dominated show which is why the Alexa Bliss vs. Sasha Banks finish was also changed. From a Bliss pinfall win it was changed to a Banks win via count-out. Still, even with that change, heels ended up winning six out of the eight matches.
Source: Wrestling Observer Newsletter