I'd really like to know where you found this sketchy info so I can check it out.
When I was WDW Cast Member piloting the Watercraft ferry boats, motor cruisers and motor launches several years ago, there was a WDW motor yacht for charter and used specifically for cruises such as you mentioned. Then, it was docked at the Grand Floridian so you might call the GF and inquire. Sorry, don't remember the name of that WDW yacht.
Be advised, I remember it as being very very 'pricey' - sorry, I can't recall any $$$ figures.
Also, I do remember at that time one of the 120' ferry boasts, the General Joe Potter, could be chartered for $600/hour with a multi-hour minimum. Sure it's probably more now. It was available for larger parties. Food/drinks additional for private parties such as a wedding reception.
Just remember, if you've got the $$$$, you are trruly Mickey's friend...
Oh, yeah, for FREE - note this all important word - you can ride the WDW Watercraft ferry boats, cruisers and launches.
Get on a Gold? Route Launch at the MK that goes to the Grand Floridian and Polynesian just before the nightly MK fireworks. Perhaps the WDW launch pilot will slow down and drift, as I would do, so those on board can watch the fireworks from the launch.
Hope this helps!