The P-51 is famous for its advanced-for-its-time aerodynamics, the prime example of which is the radiator design under the belly which utilizes the Meredith effect to, in effect, turn it into a mini jet engine. Now, the cylinder walls and cooling fins of air-cooled radials are much hotter than whatever cooling liquid that's used in the P-51's water cooler, so is it possible to produce a similar cowling for the air-cooled radials? Is there any example of such a cowling on WWII airplanes?
The Meredith effect is to recover radiator drag by using engine heat for thrust, just like a jet engine. It worked very well in the P-51 Mustang, actually adding a few knots of airspeed.
It also would work well with any source of heat, including a nuclear reactor, so yes it would work with aircooled engines.
The issue is drag from the radiator. Aircooled radials have much greater frontal drag, so it worked, just not as well. Efforts to reduce drag in the B-36 bomber resulted in roasted engines, particularly the rearward banks of the "corncob" R-4360 radial. Overheating is a major concern, as is drag. Engineers try to find a good balance.
I had to go look up what the "Meredith Effect" was (and edited your question to include a link to Wikipedia).
As I was reading through the Wiki article, I found the answer to your question:
Many engineers did not understand the operating principles of the effect. A common mistake was the idea that the air-cooled radial engine would benefit most, because its fins ran hotter than the radiator of a liquid-cooled engine, with the mistake persisting even as late as 1949. (Source)
So no, the Meredith Effect will not work on an air-cooled engine.