Partially true, but...
If we examine only part of the claim, the bit that says...
"Virus and bacteria can be killed by irradiating them with electromagnetic emissions at the right frequency"
...that part is actually true.
It is just that the "right frequency" in question needs to be so high that what you have is ionising radiation, that is to say Ultraviolet, Röntgen (X-Rays) or Gamma radiation.
Outside the human body (and other living tissue), UV, Röntgen and Gamma irradiation are frequently used to kill microbes of all sorts, and render water, foodstuffs and similar things sterile. It works very well.
Inside living tissue however, we want to avoid using irradiation, because that will not only kill the microbes, it will kill all other living tissue around it too. The operation will be successful, but the patient will die.
And that is why we do not use electromagnetic radiation to kill viruses and microbes in humans.
But what about non-ionising electromagnetic radiation?
No, we cannot affect viruses and microbes with electromagnetic emissions that are in the radio, infrared or visible spectrum, unless you consider using microwaves to heat tissue. Heat kills most germs but — again — also the unfortunate fellow that is carrying them.
In general, this kind of machine sorts under "bio-resonance" treatments and these have not been proven to have any effect on any kind of disease, propagated by pathogens or otherwise.
Lacking any scientific explanation of how bioresonance therapy might work, researchers have classified bioresonance therapy as pseudoscience. Some scientific studies did not show effects above that of the placebo effect.
WebMD states: "There is no reliable scientific evidence that bioresonance is an accurate indicator of medical conditions or disease or an effective treatment for any condition."
Proven cases of online fraud have occurred, with a practitioner making false claims that he had the ability to cure cancer, and that his clients did not need to follow the chemotherapy or surgery recommended by medical doctors, which can be life-saving. Ben Goldacre ridiculed the BBC when it reported as fact a clinic's claim that the treatment had the ability to stop 70% of clients smoking, a better result than any conventional therapy.
In the United States of America the U.S. Food and Drug Administration (FDA) classifies "devices that use resistance measurements to diagnose and treat various diseases" as Class III devices, which require FDA approval prior to marketing. The FDA has banned some of these devices from the US market, and has prosecuted many sellers of electrical devices for making false claims of health benefits.
According to Quackwatch the therapy is completely senseless and the proposed mechanism of action impossible.
So what about Rife machines?
Rife machines are fraud or — at the very kindest — deluded pseudoscience.