Would it surprise you to learn that many "Vlach shepherds" have Slavic blood? The Slavic influence of which we speak here needn't necessarily date back one or two hundred years. It could be from ten centuries ago. Thus, an alleged Vlach presence, or even dominance within a particular area, at a give time, in no way negates the possibility of a Slavic or Greek presence.
As Larisa pointed out at the very start, some in Greece are reluctant to admit that they are anything but 'purely Greek', and are disinclined to admit to anything that may point to a possible non-Greek presence in their village, city, country. Does it honestly seem logical to you that someone should neglect to so much as mention the possibility of a connection between 'Servou' and the Serbian ethnonym? How does one manage to overlook something so obvious? Bear in mind, this is Greece; it is highly unlikely that they wouldn't have herd of the Serbs. Why, then, is this perfectly plausible theory ignored? Does it really not warrant mentioning?
It's akin to a hypothetical situation of a linguist in Serbia claiming that 'Метохија' cames from 'метох(=ставих) и ја', and completely ignoring the Greek 'μετοχή' as its obvious origin.
I am not surprised at all, I have even (I believe) posted material where in many areas Vlachs mixed / assimilated with Slavs, and vice versa.