If you want the transmitter to still work after "embedding" itself into a human, then you'll have several problems.
The powder load should not be too powerful, so the bullet stays in instead of shooting through the target. This will also reduce acceleration and deceleration on the electronics.
Then, the bullet, or at least the part with the electronics, should not deform or mushroom on impact, which means it has to be hard, probably steel... which means it will tend to shoot through the target instead of staying in. You could come up with a compromise, with lead in front so it mushrooms, and the electronics behind, in a hard case.
All of this means it'll be much less deadly than a standard bullet.
Next comes the problem of frequency, antenna, and false comparison with proximity fuzes.
I'll tackle that first. The proximity fuze uses a tiny radar in the front of the shell. The electronics can handle acceleration in the gun barrel, but not deceleration at impact, since it is supposed to explode anyway. In addition, the radar uses a high-frequency directional antenna, which means most of the shell can be made of metal, with the fragile radio-transparent plastic only covering the tip where the fuze is, to let the RF beam out.
None of that applies to your idea, because you want an omnidirectional antenna so the receiver can pick up the signal anywhere, at a frequency that will go through flesh well enough so the RF gets out of the target and can be received.
So, let's look at RF absorption by salt water, which should be good enough to pass for flesh...
From this, it is obvious you will need a frequency below 10MHz, which means a rather large magnetic rod dipole antenna, which is a coil wrapped around a ferrite core. That will barely fit in a .45 bullet, and the ferrite will fracture on impact.
So, i think you will end up with a barbed flechette that stays out of the body. That would also allow to tag a car, for example. Or a bullet that deploys an antenna that stays out of the body, for example a wire coming out of the rear end. That way you can use a frequency high enough to allow for the tiny antenna that you need.
Or you could use an acoustic method: burning hot tracer bullet, and listen to the screams.