Yes, but this is qualitatively different from the AI being a 'person' whose motives you have to question. What are AlphaGo's motives?
An AI judge will be optimizing for the things that we build an AI judge to optimize for, the things we find desirable in our legal decisions. Consistency with past rulings, not issuing judgements that open up tricky interactions with other laws/judgements, erring on the side of caution when the sentence will ruin the defendant's life, etc.
But it still won't have "motives". We won't wonder if it issues a particular judgement because 5% of its investment portfolio is allocated to pharmaceutical companies, or if it believes that the USA would be a better place if all the black people "went back to Africa".