This may be a little lengthy so bear with me.
It may be helpful to know the definition of a resident alien in order tohelp answer your question.
A resident alien is an individual that is not a U.S. Citizen or National of the U.S. and who either meets the green card test or the substantial presence test for the calendar year. The individual is a lawful permanent resident of the U.S. if at any time during the calendar year the alien held an immigrant visa ("green card") or The individual was physically present in the U.S. on at least: 1) 31 days during the calendar year; and 2) 183 days or more during the current year and the two preceding calendar years. If they meet these guidelines then the W-9 is required, otherwise the W-8BEN is required for each owner on the account.
For additional information reference IRS Publications 515 and 519.
I hope this helps.