No, he’s not a relative of Siam Sam. 
But the hunt is on for the identity of Siam Joe after an old photo album containing WWII photos from Thailand and the vicinity surfaced in London.
Story here.
Excerpt: **"An old photograph album donated to a charity shop has sparked a mystery over the identity of the photos’ subject.
"All that is known from scant information scrawled inside the 20-page album is that he served with 20 Squadron RAF during the Second World War and referred to himself as ‘Siam Joe’.
“Carefully-mounted pictures show him in uniform as he stands in front of some palm trees with his hands on his hips and with his squadron and aircraft. Even his ration packs are recorded for posterity.”**