I think it was fboab who wrote a post with a comprehensive (though by no means complete) list of things that count as cheating, including many which were contradictory.
Sure, electrons are cheating, but so is training, or riding a lightweight bike, or having the right amount of air in your tyres, or using clipless pedals, or being male, or using an off-road bike, or drafting another rider, or... <fx: fade out>. Personally, I think the whole point in bikes is cheating; it's how we avoid having to do Running. And really, if you're not actually breaking the rules of a race, who cares?
'Cheating' doesn't bother me in the slightest when used in a tongue-in-cheek way like that. It's like the accusations of taking it easy[1] or lying down on the job - or indeed cheating - that you get when you ride a recumbent. But I'm aware that some e-bike users - particularly those with disabilities - can take offence at it, so I'd avoid using with someone I didn't know.
(Barakta's response to being accused of cheating is to give a hand gesture that moves from the BSL for <electricity> into a V-sign as she shoots past and disappears up the inevitable hill. Seems fair.)
[1] This one's a bastard, as you're then obliged to continue making it look easy until you disappear from sight, which inevitably involves climbing a hill.