Re:
At top-level bikes are weighed; but as the racers are underweight and have to have weights added to meet the UCI minimum weight limit, there's scope for adding in various parts and not showing up as 'suspiciously overweight'.
Looks like there was a bike with a motor in at Zolder; and caught by the officials - but still not been confirmed whether that bike was raced, and whether the specific bike tested was even approved to be raced at that event.
Interestingly there have been suggestions for a few years that these lower level series are a potential testing ground for 'cheating technologies' as there are fewer tests and officials than at top-level events.