We stayed at Ludington two years ago. You can fill at the dump station but you can't fill from the water spigot inside the campground itself. A hose just won't fit. Never used a water thief but after a quick glance, it doesn't appear that it will fit onto the spigots at Ludington. I think the spigot is too wide to accommodate that.
To refill our fresh water, we use a large soft tank that can go onto the top of your tow vehicle. We fill that with clean water, then let it gravity feed into the TT. Works great for the MI state parks, b/c very very few have water on site.