Yes, you will. There's a possibility of wiggle room at MGM Resorts International, where they are "still finalizing details about the [parking-fee] plan" but cannot disclose anything at this time. The Cosmopolitan has promised to maintain its free-parking policy, regardless of what the competition does, and the Stratosphere is now proudly trumpeting free parking. Although valet parking is mandatory at MGM's Vdara hotel, it's free for the moment, as is the case at Trump International, which has no self-parking and once charged for its valet service, but ceased to a few years ago (regardless of whether you're a guest or just visiting the property). At Vdara's CityCenter neighbor Mandarin Oriental, however, it's $20 a night, no exceptions.
A semi-random survey of downtown casinos found that those who charge for parking do not discount their rates for handicapped patrons. On the bright side, parking charges are generally low: For instance, the Plaza Hotel's parking is free for guests, $2 an hour for visitors. Both the California Hotel Casino and Main Street Station charge $3 for self parking to non-hotel guests Monday through Thursday, upping it to $5 on weekends, but that fee is reimbursed at the cashier's cage to diners who present a same-day restaurant receipt of $5 or more and the parking-kiosk voucher, and to B Connected members of a high-enough rank, or who fulfill the minimum slot/table game play requirements. Registered hotel guests, meanwhile, receive a parking permit upon check-in to present to the parking attendants that absolves them of paying a fee. (Should you lose/forget this, present your same-day kiosk voucher and proof of stay at the cage for reimbursement.)
The Downtown Grand hits you up for $5 Sunday through Thursday and $10 on Friday and Saturday for valet (waived only if you're a Platinum or Black-tier member of the Downtown Grand Rewards Club player-loyalty program), but self-parking is included in the resort fee ($22.34/night, inclusive of tax). If you're not a hotel guest and are visiting the property to dine or play, self-parking is $6 for up to two hours, $12 for 2-12 hours, with no discount for handicapped drivers. (The baroque ins and outs of downtown-casino parking policies are chronicled here.)
So, in conclusion, we could find no evidence of special fee consideration for disabled casino patrons, nor any likelihood of change. On the upside, for the time being at least there are still plenty of hotels and casinos all over town where parking remains free.
