I think you'll find "clientism" is a function of the unemployment rate. When people are desperate for jobs, clientism will rule. In the real immigrant regions of Rotterdam for example, there is near 100% clientism. By which I mean that every dishwasher is there because they're related, married or very close friends (rare) to the owner.
Not that it doesn't happen in The Hague in the big banks, it does, especially higher up. But once you get lower than director, there is very little of it left. There is essentially no unemployment among the educated Dutch population, and they would never do the clientism thing ... at least not for an entry level job. Where you really find it is when big companies outsource local functions, like cleaning the office, or buying large amounts of furnishings. When you look at the personal relationships between those businesses, that's where you go "wait a second ... I've seen that name before".
With 30% unemployment, of course you try to help your family with a job, especially if that's the only way to survive. And that pushes out everyone else at that level of unemployment, of course.
With 4% unemployment. How low is that ? Well, there are ~10% people with an iq < 80, in any population, which is the level where you have to repeat instructions every 2h at least. Not once, not 10x, not 1000x, but every last 2h. Nor are these people capable of correctly carrying out simple written instructions, so you cannot hang them on the wall and expect anything but disaster. (75 is considered handicapped to the point that they cannot be left alone, ever).
In the Netherlands, half of such people are employed in private businesses. That's how low the unemployment rate is there at the moment.
So no, with that sort of competition for workers, there is very little clientism at the lower levels of companies.
But this has very little to do with cultural differences or attitude differences between the Netherlands and Greece. I'm sure they mattered for the first 2 months of the problem, those differences ... perhaps ... but not for very long. Under the same pressures, the Dutch would surely do the same as the Greek.