I have only worked for a single company, and it's a very international. Everyone speaks English. There is close to zero written or spoken Dutch.

This is in Amsterdam though, where a lot of people both within my company and outside speak English. If you go else where in the country, outside of North Holland, people defiantly speak less English and it's more advantageous to know Dutch.

I personally learned Dutch because I didn't feel like I could really assimilate without it.

Most companies don't care that you don't know the language (and aren't planning to). But you will need to learn it to fully integrate in the country (though many haven't and do fine).

I've lived and worked in the NL for 6 years. It depends on the company. Most companies I've worked for have not minded at all that I wasn't fluent. Some companies will be happy to offer to pay for language courses.

I think you'll find that most tech companies in the west of the country won't mind at all, but in other parts of the Netherlands it can vary.