Short Answer: No. But it really depends on context.

If the context is that this will prevent police from digging up a body as part of an investigation into a crime, this will not work. On the off chance that the police are even aware the plants are endangered, there will be legal avenues for relocating or otherwise disturbing the plants. A criminal investigation involving a human body is something that is going to qualify in most parts of the world.

Overall, it's an idea that sounds smart or funny, but when you break it down, it's not particularly likely to work out.

You can't just plant any ole endangered plants over or around the site. You would have to select plants that are endemic to the area and which specifically are adapted to the conditions at the site where the body is buried. If the endangered plants aren't native to the area, then they aren't going to be covered by any laws that would make them illegal to dig up because it would be clear that they aren't wild plants. And if you don't match the plants to the specific conditions at the site of the body, then they aren't going to survive and thus would offer no protection from being disturbed. Also, endangered plants are usually endangered for a reason, it's not going to be as easy as digging a hole and plopping a potted petunia down into it. You'd probably need to provide some degree of after care to ensure the plants survive long term, which is going to substantially increase the chances of the body being discovered. And that's all assuming you could even acquire the endangered plants that would work for this purpose or that there are any such plants.