Yes, of course, but if the tarp comes off a bit early, more snow is accumulated on the field and it makes the conditions worse. If you are the home team and knew you were going to do this going into the game, you can adjust your game plan accordingly. I'm not saying that it was the reason the Raiders lost at all though. Gruden was well aware of the weather conditions that day. And AV implied that it wasn't the first time Bill/Kraft did this - "Bill does whatever he can do get an edge in a game, and sometimes that means crappy field conditions for me."
In any event, this whole Chiefs groundskeeper helping the chiefs in the SB makes little sense. First of all, the person in charge of the whole field was the NFL's field surface director, Ed Mangan. Second, why would you deliberately make the field more slick when your starting QB has a badly sprained ankle and could easily slip and make it worse? Mahomes was definitely slipping out there. The truth is they wanted the field to look good on TV, and unfortunately, it led to slick field conditions - that's where the problem lies. The league is ultimately responsible.