Seems that my maternal line (Hemer/Hemmer/Hemr) from Chysna / Pehlrimov area were knackers by occupation. I've fortunately found a Hemer/DNA relative in Prague who enlightened me somewhat as to the unique cultural situation for knacker families. They processed dead or sick animals. They had freedom to move and not tied to a farm, estate or a "lord". They were generally "unaccepted" in mainstream society but not exactly outcasts. Marriages were usually between knacker families.
Does anyone know of availability of other information on knackers?