"It is possibly him."
Translation:Mogelijk is het hem.
The correct Dutch translation, in my opinion, would be "Mogelijk is hij het", because "hem" is used where "he" is the object, accusativus, or "lijdend voorwerp" in Dutch. In this sentence however "he" is not the "lijdend voorwerp", but the so called "naamwoordelijk deel van het gezegde", that is to say "It" and "him" are both the same person, the "him" is not having something done to him in this sentence but rather the sentence explains what he is (namely, "it", in this case). Therefore "he" is inflected as a subject, nominativus or "onderwerp". In fact I think one could complain about the English sentence being not quite right grammatically, but the English do not care so much about their cases which is fair enough.
In brief: it should be "Mogelijk is hij het" for grammatical reasons.