Your link not working for me, but maybe it's just me.
Here's another link to the MGM / MLife Parking Policy -- starts June 6.

http://www.mgmresorts.com/parking/

Not so bad. If you have any MLife players card, even entry level, you can still self-park for free.
Free Valet parking takes higher level card.
Special rules for Locals (just a drivers license) and for hotel guests.

The only parking lots with stricter rules (i.e. pay parking) are the ones closest to the new arena behind NYNY ... during an event at the arena.
Specifically, NYNY, Monte Carlo and Aria. That makes sense.

Of course, policy may tighten up in the months / years to come.