Can a person with a dependent visa work in Poland legally ?
Only if they can find an employer willing to go through the process of getting a work permit for them.
Again, no one is asking whether they have the ability to get a job.
Which is their big mistake. That should be the very first question. No point in discussing legal fine points with someone who does not have a snowball's chance of ever getting a job in Poland anyway. That's a total waste of time and energy.
If you want help and advice, then make sure up front that there is a good reason to ask it.