It really depends on what sources you use though. Sure, MODERN 'Merlins' are typically seen as wizards, but if you go back to the Celtic sources, they're much more like advisors, peace makers, and a sort of 'priest'. Its really unclear what the historical druids were, we really have nothing more than a couple paragraphs about them. So, yeah, it may be that the D&D druid owes something to neo-paganism, though I wonder which way the influence actually flowed...
I mean, I was around in the 1960s, and while neo-paganism WAS achieving some level of profile at that time, I don't think it had a huge impact on D&D. IME the confluence was more in the '80s when there was a LOT of crossover between D&D and SCA groups and such (of which a fair percentage were also Wiccans). Of course, not knowing much about Dave in that respect, it is quite possible he was inspired by neo-pagan sources or was himself exposed to it.