Actually, I hadn't read this poem in years until these posts got me intrigued again . . . so I just dug it out.
The poem is about a king whose hubris rose to such a pitch that he set himself above all other concerns. When the signs of his folly became obvious to all but him, his "Knechten" rose up and killed him.
The poem describes the "Knechten" as feasting in the King's hall and draining their goblets of wine . . . so this is definitely a reference to senior retainers (ministers and generals?), not to slaves or servants (revolutionaries?).
If those lines were written on the wall at the Ipatiev house to make a point about Nicholas' death, it was not the tale of a Jewish conspiracy. It was the tale of how Nicholas was brought down by his refusal to deal with a situation that his ministers and generals saw far more clearly but could not get him to heed.
Whoever would have known this quote was certainly educated enough to have grasped the meaning of the poem.