You are very wise to question the information on all these trees. Unfortunately people find a tree and copy it into their own without verifying the details, and it doesn't take long for an error to proliferate among dozens of online trees.
In order to attain the degree of MD (Doctor of Medicine), you have to submit a thesis to a university. If Neil Cameron Sr did indeed have an MD degree, it should not be too hard to find him as there were only four universities in Scotland (St Andrews, Glasgow, Aberdeen, Edinburgh) plus two in England (Oxford, Cambridge) in the late 18th century.
However just because he was a medical doctor does not mean that he was actually an MD. The basic medical degree is Bachelor of Medicine and Bachelor of Surgery (MB ChB or similar). Again, if he was MB ChB he must have studied at a university, and the universities would normally have information about all their graduates, usually including where they were from and the names of their fathers.
There are printed tomes with lists of graduates of the University of Aberdeen.
There are lists of graduates of the University of Glasgow at
https://www.universitystory.gla.ac.uk/browse-graduates/ but there is no Neil Cameron listed.
For St Andrews and Edinburgh I think you might have to contact the respective university archives.
On the other hand, I don't know when it became obligatory to have any formal medical training at all in order to practise as a medical doctor.
Nor do I know of a site for searching early 19th century medical practitioners.