Correction: In Ukrainian it is "Stanyslav" because it's written as "Станислав" Ukrainian letter "и" equals "y" in English and Ukrainian "i" equals "i" in English. [transcription fixed -ed]
Stanisław Modzelewski was a Polish serial killer known as "The Vampire of Gałkówek" active in Łódź, Poland during the 1950s. He completed three classes of primary school, he was a driver by occupation and he worked in Warsaw. In the period of 1952-1956 and in 1967, he murdered seven women and attempted the murder of six other women. Although he is believed to have murdered another, eighth victim, it was never proven, as the body was never found. He was sentenced to death and the execution by hanging, which was carried out in November 1969, in Warsaw.
Maybe some Polish-Americans might have used this as a Polish form of Stanley in the past, but not anymore. This name has no relation to the name Stanley, and is never used as a form of it in Poland. [noted -ed]
In Polish, stan does not mean "government" or "camp", it means "state (condition)". Therefore, this name would most likely mean "glorious" (a state or condition of glory).