As a full-time diorama builder, I'm not in favor of animating anything on a diorama.... So much for motorizing props... It removes completely the "Snap-Shot Effect" that makes the diorama truly what it is, a 3-D "photograph"... While "neat-o", it's just not something that'll win you anything in a competition except perhaps, "Modeler's Choice", if there even IS such a category anymore...
Onto the "Prop-Blurs"... While they're closer to what we, as diorma-builders want, only if you trim them exactly right, and then paint them exactly right (if you're doing the prop-tips in yellow, for instance) will they come through for you... Most guys fail to trim them them to varying widths, electing to put three or four little "battle-axes" onto a prop-hub, rather then get that "random" look...
So, I'm in favor of using a clear prop-disc, and for several reasons. One, the blades and tips are translucent, as they should be. Two, the blades can be simulated with ever-widening "Wisks" of cement (Testor's Tube or Black Bottle)... Three, they're far easier to paint.. First, mask the outer-edge of the disk (where the yellow would be)...
Using transparent Black and Transparent Yellow (available from Createx Airbrush Colors), you just airbrush the afore-mentioned "wisks" with Black, getting it a little bit heavier in the center, where the blade's at, then after that cures, remove the mask and airbrush the yellow tips ALL the way around...
You got a "spinning" prop...
But there's another consideration for your particular diorama idea, Ace.. The PBY, or if it was Army Air Force, an OA-10, would shut down the engines while making the rescue, since the survivor(s) will be loaded into the aircraft from either the waist-blisters (prop wash wold make it quite difficult for even an unwounded and healthy aviator to get close enough to be picked up by the crew), or the nose, and you don't want spinning props righ above your head while you're gettin someone into the hull there..
A sea-anchor was used to maintain station-keeping during a rescue, if needed, and that was also deployed from the nose... This USAAF OA-10 is anchored at sea off the coast New Guinea, and you can see the flight engineer is about to load the Coffman Starte in the port engine...
This is the best picture I could find of seven Merchant Marine suriviors being loaded into a PBY at the waist, after they'd been torpedoed in the Atlantic: