Two words: Gruber Assist. Check it out. The commissaires can do random scans now on bikes, and so far all the scans have produced - nothing.
I think Gruber Assist and Vivax Assist are the same thing - either Vivax have taken over Gruber or they are marketing it as Vivax.
Never mind scans, the commissaires stripped a lot of bikes after one of the classics - seatpost out, pedals and crank out - and found nothing
It doesn't seem to me that the 'stealth' kit as advertised would really hide the equipment to the level necessary for mechanical doping - some details would still be visible to an interested party even on just a close look round the bike. It wouldn't be difficult to genuinely stealth it though, particularly if you have tame frame makers etc.
Looking at the kit I wonder how reliable these would be (for a leisure rider) in the long term, and whether you'd run out of battery if using it a lot in one day - the motor mounting doesn't seem particularly secure, and the batteries aren't big. Still, won't be long before someone adds regenerative braking or finds a way to charge it on the downhills...