I don't think it's a bad strategy at all. Splash did it as well. But Splash also set up the story and introduced the characters on the ride. It was impossible to miss unless you chose to ignore it.
With Tiana, it's not so much the story that will confuse. It's the characters that aren't formally introduced. For us Disney fanatics, we know it all going in. For some general folks, especially kids, I see how they might be confused.
I suspect most know of Louis and Princess Tiana, but many will question the outfit change. The new critters are not introduced/referred to by name at all on the ride, not that it's necessarily an issue. I think Mama Odie is the biggest one though. If you haven't watched the movie, you probably don't know who she is or who she's affiliated with. I saw a POV from ResortTV1 and their kid pointed at Odie saying "Who's that? Is she the bad guy?". And quite frankly, I am not surprised at how someone would come to that conclusion with zero context given. She randomly shrinks you halfway through the ride, then tosses you over the scary waterfall whilst cackling at you.