The question of what "researcher" means comes down to whether you are performing work, or are a student. US tax laws treat income differently whether it is "earned" (from performing a service) or "unearned" (which includes prizes and grants). If you are in a learning or training position (such as graduate student or postdoc) then you are technically a student and you are not performing "work" in exchange for compensation. It is unearned income, even though what you do "feels" like working (you go in every day, you perform experiments, write reports, and so on. The student designation generally applies to graduate students and post-doctoral fellows. The university can write you a check and all the tax consequences are on the student.
In any position that is considered "working" (earned income, you are an employee and your employer sets the terms of your work) you will be treated as an employee. The employer must report your pay on a W-2 at the end of the year, and withhold federal and state income taxes and social security and Medicare taxes. This is true regardless of your residency status. As an employee, your employer may also have additional responsibilities under state law, such as to provide certain mandatory minimum benefits, follow wage and hour laws, and so on.
I have been a technician, grad student, post-doc, research associate, and faculty in my career, and have a pretty good understanding of of the tax status of each.
"Research associate" is probably a staff position, not a student or training position, although you will need to check with HR if you are not clear. As such, you should expect to have taxes withheld from your pay and to receive a W-2 at the end of the year with which to file your tax return.
Hope this clarification helps.
I can't address your residency status or tax treaty status without doing a lot more research.
As a result of the Patriot Act after 9/11, US banks must verify the identity of their customers. You can give them a W8-BEN instead of a W-9, if you think you are not a US resident for income tax purposes yet, but when you become a resident you will need to give them a W-9 anyway.
