This depends on a lot of things, such as what the illegal activity is, whether they were told to do it, whether they knew it was illegal, and so on.
In this case, it's a product sale regulation. It's not illegal to manufacture non-compliant engines, but it's illegal to sell them. So in a world of individual-only responsibility, that would make the individual sales agents who performed the transactions with customers liable. I don't think that's an improvement.
(This answer may change if the sales agents know or should have known that the product was not legal to sell; this definitely applies to e.g. sales of alcohol to minors)
