I frequently visit Woodhall Spa and sometimes eat/drink at Petwood Hotel, ex- the Mess.
The story is well known in the town. I first heard it in the super bookshop, where Nigger was said to have been present at the unveiling of the memorial in the town centre, but failed to appear when the photos were developed.
People will believe what they want to believe. For myself, I have had a few experiences which are difficult to rationalise, so I suspend disblief.
Certainly when I was P Met O 1 Gp. Bawtry c. 1982 with oversight of Scampton [and 10 other RAF bases] for their Met. the grave was well tended and clearly marked.
By the way the "VC" on the dog only vaguely resembles the real thing, totally unconvincing, came out of a Christmas cracker more like!