I am curious if it would be possible to continue learning Polish while I'm there. I do not speak Dutch, so the Polish courses offered (at least those I found on google) are not possible for me.
There are Polish language lessons available in Amsterdam.
The People's University (Volksuniversiteit) runs part time courses for adults and has a branch in Amsterdam. They only put the courses on if there's sufficient demand so it would make sense to contact them as soon as possible to indicate an interest.You would probably need to improve your Dutch first, a good idea if you're going to live there.
Your best bet is to find a private teacher who also speaks English. Ask at the People's University - they presumably hire teachers from time to time and may be able to refer you to one of those teachers. A better bet could be the Forum Szkół Polskich w Holandii. It's aimed at children but you may well find one of their teachers is willing to do private lessons and is also an English speaker.
there are numerous Polish immigrants in and around Amsterdam who'd love to finally learn Dutch
Doubtless many, however English is very widely spoken in Amsterdam. A Russian friend, fluent in Polish went there to work. He told prospective employers that he'd learnt Dutch. Most said that was unnecessary since all their staff and clients all speak English.
Scots isn't a "separate" language
Yes it is. Just as Walloon is not a dialect of French.