Yes there is! If you've purchased any of the Harbor Nights tickets, there's complimentary self parking in the resort's parking garage or discounted valet parking available just by puling up to the front of the resort. (There's little signs on the driveway leading to the resort, so just follow those to whichever location you want to park in).
I don't know exactly how much the discount is if you decide to go with valet parking. I've never used valet parking at Portofino Bay. The self-parking garage is kind of tight if you have a really large vehicle — but I think it's kind of fun driving around up and down the different levels.
I will say though — self parking is much easier if you arrive say, 45 minutes before the event begins. Quite a few people do show up for a Harbor Nights event — and that's on top of all the other guests staying at the resort. If you're pulling up 5 minutes before the event starts… parking is going to be hard to find in the self-parking area.
If you're already staying at the resort — the free parking or discounted valet parking is not available. I have no idea what that actually means — I've never actually been staying at Portofino Bay when a Harbor Nights event was going on — but it's in the fine print on everything that they publish about Harbor Nights — so I thought I'd pass that info on.