Officers don't get tasered as part of their training.
I asked that follow up question to find out if you think officers should get batoned as part of their training? Given that batons are less dangerous?
I think a baton carries a much more higher risk of injury than taser and a study in Canada supported this with instances of hospitalisation far higher after baton usage than taser usage.
In terms of lethality, yes taser carries a higher risk - but this higher risk is alongside an already high risk situation. Taser has been used in the UK for well over a decade and it's been used a bucket-load of times in that period with only a handful of cases of the taser discharge being found to be unnecessary and even fewer resulting in the death of the person of it being used on.
And since you mention CS spray, I don't know about you but I remember back in the day when all the officers where issued with CS, there were similar lethality debates. The theory being the extreme pain and panic caused by CS could exacerbate an existing cardiac problem (exactly the same argument for taser, but with the electrical element instead). And yes, this has contributed in the deaths of a few people. But unfortunately, you can't always be aware of how someone is going to react to any use of force. I know of a police officer who merely told someone they were under arrest and the suspect collapsed and suffered a fatal heart attack. That is technically a death in police contact.
Anyway, back the topic - tasers. Not perfect but there never is perfection when you're trying to stop a suspect who presents significant danger to themselves or others.
If tasers are safe enough to use in non lethal scenarios then they should be used in training on the police officers using them... If they are considered too dangerous then they should not be used for non lethal situations.