This surname is by no means exclusively Dutch. However, I've personally always heard it pronounced with a long 'o'. So as in the first one of your suggestions, I think.
But it could easily be that the short 'o' can also be heard. We have for instance the word "promenade' (I don't know the phonetic spelling) which is often pronounced with a short 'o'.at least in the Netherlands. I don't know why this difference exists. Maybe someone else does.
Wikipedia says "Weakly stressed long vowels may also be shortened without any significant reduction in vowel quality. For example, politie (phonemically /poːˈlitsi/) may be pronounced [poˈli(t)si], [pəˈli(t)si] or even [ˈpli(t)si]."
Do you think it is a case of it?
I've listened to it again. It sounds like a long 'o' to me now. Maybe pronounced a bit 'in the back of his mouth' (I don't know the appropriate term). I'm not familar enough with phonetics to confidently answer your specific question.