Cop do a lot of thing that's deem illegal if done by normal people, like speeding and weaving in traffic and shooting at unarmed people. They ain't gonna stop at destroying an endangered species just to dig up bodies that you hide last summer, right between the gnome and the flamingo you used to mark the place.

Exceptions to rules almost always exist.

It's sad that I know this, but no.

Years ago, I buried one of my guinea pigs that had died. I dug the hole really fucking deep, but each night our lawn was getting brutalised by foxes or whatever tried to dig holes in the night. One night I looked out, and saw multiple animals digging at the hole.

I mentioned this to someone at my gym, and one person chimed in to say that they worked in forensics. Apparently lots of dead bodies are dug up either partly or fully by animals that can smell the body, so much of what they had to work with was tainted by animal markings. The animals might not smell below the ground, but you probably dug the hole with the body nearby...

TLDR: Animals don't give a heck about the law.

for your dead friend?

Nah, the real trick is burying the body deep deep, then burying a dead animal a few feet above it. Corpse Dog hits, but they dig up a sheep, Lt. Scruffins ain't gettin a treat

Because something is illegal, it doesn't mean police couldn't do it anyway.

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.

Kinda makes sense in a way. Like here in CA, it's big trouble if you mess with a Joshua Tree, especially little ones, to the point that most people don't wanna go through the paperwork to deal with them. If you can make it look like it was always there (or just grew there naturally), I don't see why not.