Zel and Shelley:
I'm not sure I understand Ruel's point.
I think he is asking whether "Visayan" refers to a geographic region (i.e., the Visayas), or whether "Visayan" applies to members of ethnic groups that traditionally populated that geographic region (whether or not they presently live there)?
To avoid confusion, it seems that one has to limit the definition both geographically and ethnically. That is, apply the term to ethnic groups who live primarily within the Visayas. That excludes immigrants to the Visayas whose main ethnic homeland is elsewhere, and native Visayans who live outside the Visayas. You can lump and split such groups a thousand different ways, but if you stick with the ethnic groups that have been in much the same place for a hundred years or more, then you have some stability to your definition.
Clarity and simplicity of this definition will make your research much more straight forward, and ultimately more understandable for you and your audience. It is inevitable that somebody will have a problem with whatever definition you use. I don't think that matters very much, as long as you can communicate exactly how you defined and used the term for your study.
Ian.