Sorry to hear about your dad! (Had an uncle that suffered from Parkinson's. It's pitiful condition :(. )
Although there's been extensive research, the only studies concluding that there's a link between neurological phenomena and EM at non-instantly damaging levels, were a rather ethicallly questionable study from the early 1960s and some not-very-convincing work in the 1970s. There has been some reports of auditory sensations near active microwave transmitters, but these are usually explained by "the field is strong enough to heat your brain or auditory sensing organs significantly".
I don't see a direct correlation to Parkinson's and dementia. Considering Wullenweber arrays are receivers, the EM levels at the antenna site would be extremely benign. The receiver processing and amplifier stations, although probably full of flame-retardants, refrigerants, building isolation material and heavy metals of negative health effect as any electrical building in the mid-twentieth century, should probably not have had significant levels of EMI, either, because that directly conflicts with the need for a low-electrical-noise environment of such receivers.
I'm not a neurologist, so I will abstain from making any diagnosis of a person I've never met – but Parkinson's, as terrible as it is, has a prevalence of 0.3% in industrialized nations: 3 in 1000 people have it. Dementia is a common complication in later-stage Parkinson, sadly, but could also have arised separately; it's not a rare disease, either. There are environmental factors which are known to be correlated with dementia (e.g. exposure to lead and other heavy minerals), but given the information you gave in the question (your dad not being a painter, or handling a lot of mercury), I'd avoid jumping to conclusions here. My best explanation for your father's illness is probably really really bad luck :(