There's a low probability, but it can't be excluded that the last name Sadkov traces its origins to the name Sadko (or Sadok).
It has a Hebrew origin and is formed from sadok / ztadok, which translated to Russian means "a just one". Based on this hypothesis it can be reasoned that the parents named their child so as to honor the legendary hero Sadko. According to the ancient epos, Sadko was a poor gusli player who enchanted the Water king with his music, which he used to quickly
get rich and become a merchant. During a storm, Sadko ends up in the sea king's hands, he starts to dance to the sound of his gusli and that the sea starts to billow, so saint Mikola the Graceful arrives to help the dying people and ships.
http://www.ufolog.ru/names/order/Садков