Everyone is encouraged to volunteer for the chapter , regardless of what his or her day job is. There is nothing that prevents even a foundation staff or contractor even being the board member of the chapter , less alone any volunteer or member. There are several Wikimedia chapters in the world who has paid and full time staff working for them. The Secretary ( volunteer) of the Dutch chapter is also a Foundation Full time Contractor.
Hope that clarifies
I'm not sure what you are talking about above.
The issue with Siebrand is a conflict of interest, as far as I know, they should/would have declared it to their members. Laws in several countries dictate that board of non-profit can not be paid employees of their own or parent organizations. Several chapter board members usually resign to take up employee position. It used to be that they had to resign to take up any position as staff, but contractor is a relatively new feature with confusing legality, but there are still individuals who see the distinction and resign or declare their conflicts upfront. Board members by definition can not be paid employees, this is not my distinction but a legal one. Something I believe all WIkimedia organizations should adhere to.
I believe Ashwin explained it much better than I could. If we can demarcate what role someone does something as, it would help a lot. The community staff at WMF usually keep 2 accounts to demarcate this clearly, on wiki.
It might not be "practically separate whether we does something as a volunteer...." the distinction is actually quite simple. One that en.wp, staff and majority of the community holds- paid vs. non-paid. What one does as an employee is separate from what one does as an employee. That is why they have two accounts and rather large disclaimers on their user pages, demarcating this very difference.
Regards
Theo
P.S. @achal lol