Charles Ellicott Commentary Deuteronomy 32:31

"For their rock is not as our Rock, Even our enemies themselves being judges." — Deuteronomy 32:31 (ASV)

For their rock. —Perhaps this may be understood as: For their rock (the enemies’ God) is not as our Rock (Jehovah), and yet our enemies are judges, i.e., lords, over us. Rashi interprets it this way. The verse should be read as a parenthesis. The argument would be this: No cause can be found for the defeat of Israel except the displeasure of Jehovah. The enemies have no gods that could fight against Israel.

The word for judges occurs only in Exodus 21:22; Job 31:11. The phrase “our enemies themselves being judges” (of the question) is more like Latin than Hebrew, but it may be correct.