I wonder whether he could have been named after someone the family admired, rather than being related?
I've come across a Capt William Darling Dawson who was from Hartlepool, but was based in Peterhead before he emigrated to Australia and New Zealand. He married a Peterhead-born lass in 1871 in Australia. She was Matilda, daughter of the late Capt John Johnston (and Mary Lane of Limerick).
http://trove.nla.gov.au/ndp/del/article/13245121?searchTerm=&searchLimits=l-publictag=NEBEA
