Ok, so I work in a school (private, overseas) that does online Zoom lessons - private server etc to avoid the trolling, strict safeguarding protocols etc. We don't have a 'one computer per family & mum needs it to WFH' situation, either - our kids all have a laptop & a smartphone as a minimum. Because they come from wealthy families.
So none of the perfectly valid reasons for not teaching 'live', which limit its use in state schools in the U.K., apply here.
Nonetheless, after the first fortnight of lockdown shortly before Easter, SLT realised that teaching a FT timetable online was not conducive to staff wellbeing, to put it mildly. More importantly, tbh as far as SLT were concerned, the parents were kicking off! Too much screen time, impossible to supervise whilst working themselves, kids with disrupted sleep patterns, everyone stressed out over Coronavirus, etc etc.
So we went with a new timetable. 4 lessons per day not 6, so subjects like mine that usually get 4 periods a week were down to 2 or maybe 3.
The expectation was that up to 50% of the teaching was live via Zoom, so for example you could do a 20 minute discussion, set work, & unmute Zoom again for a 20 minute plenary. You were also expected to monitor Zoom so struggling kids could get help via chat.
The other lesson you set work for. This might include making a video talking through a PowerPoint resource for kids to watch in their own time. Basically, the idea was that everyone could manage to be online for a couple of hours a day at set times, but the rest was independent.
So my working day might look like this: teach a class, 2 hours with nothing I needed to be doing live, teach another class, spend the evening recording stuff for other classes/marking work online. Often till the wee hours.
I was doing everything the SLT asked of me, & everything the parents asked of them. So if I'd wanted to tutor in the 2 hours in the middle - why not?
As it happened, NO chance! 3dc of my own to keep on top of. It was murder.
But I had colleagues who did - not our students, obviously - & it was absolutely approved by the school. SLT were appreciative of the fact that we were delivering high quality education & the parents were all happy.
It was also understood that many of us had lost out on work examining (I'm down £3k this year).
Anyway - long post! But the point is: if a teacher is 'moonlighting' in breach of their school's policy, or to the detriment of doing their job to the SLT's satisfaction, then obviously they should be disciplined.
If they are discharging their responsibilities whilst juggling their hours, & this is not a breach of their T&Cs, then it's nobody else's business.