I agree but the term 'class traitor' does not appear in Marx or Engels texts because they do not discuss individual 'guilt' or any form of individual morality, they discuss the overall econimcal and societal relations to each other.
Class traitors as a term appears later in revolutionary rhetoric and it usually describes a conscious effort against the interest of the own class. Soldiers act within the power structure of the state, not as free actors representing their class. Their role is institutionally dictated, not a individual ideological 'betrayal' like for example union busters.
With the term lumpen Proletarier Marx himself describes something similar but different. The Lumpenproletariat according to Marx does not live within the structures of typical class, they do not own means of production, but they are also not giving their labor for a wage. Through that they can not have a unified class consciousness and act largely indivualisticly. He means economic minorities like beggars, vagabonds, criminals, grifters and the like. According to Marx they are 'politically unreliable ' and usually reactionary in nature.
It's worth noting that this kind of classification was criticized widely, the term itself is seen as problematic even within Marxist circles.