The Dutch did hire Japanese to fight their wars. I wrote about that here. I should note trade was restricted to Dejima (Nagasaki) and Hirado (which closed down when the English East India Company pulled out), but was not banned (except for a short stretch around 1630). The Dutch would be the Europeans to trade with Japan throughout the Edo period.

For the final conquest of Banda island in 1621, there were 87 Japanese on the campaign. According to wiki the Dutch fleet arrived at Banda in late February. The Edo bakufu issued orders disallowing Japanese to leave Japan and disallowed recruiting of anyone, mercenary or otherwise, without Edo's permission also in February of 1621. Given the timing then it would have had no effect on the Banda campaign.

It's harder to tell if these men would have been "samurai" or even "rōnin" in Japan. It's certainly possible some of them were. But it's unlikely all of them, or even most of them, were. Of the 11 Japanese involved in the Amboyna incident of 1623, 8 were from Hirado or Nagasaki, while the other three were all from near-by northwestern Kyūshū. Only two are old enough to have possibly participated in the Sekigahara campaign. Though most are old enough to have participated in the siege of Ōsaka, and certainly not ruling out the possibility of being born to a warrior family, by their age and birth place most hires probably had no military experience before going abroad. Most were probably of opportunity, people searching for opportunity abroad and/or (for some Christians) escaping persecution at home.