Lizzie,
No, this individual is another crew member with the same surname - not as far as I know immediate family. Since I last posted here I have indeed started a new thread on The Common Room to ask the more general question about whether opposing Navies picked up survivors from the other side, and have had a very generous and knowledgable reply from a Rootschatter called Larkspur. I'm gradually getting a different picture of the aftermath of the carnage on that day on May 31st 1916, a much better, more positive one.
And thanks so much for putting all that precise detail on your penultimate post about all the survivors themselves..
Keith
…and will certainly keep an eye on that link you've kindly provided for any updates on new records...