grammaticality - The use of nominative "whom" (as in “persons whom it is foreseeable are likely to...”)

From page 48 of Law: A Very Short Introduction, by Raymond Wacks:

In other words, you owe a duty to persons whom it is foreseeable are likely to be harmed by your conduct.

To try to parse this, temporarily overlook 'it is foreseeable'. Then persons is the subject of the verb phrase are likely to be harmed. So according to this question,
should the relative pronoun for persons be who instead? Is my parse wrong?

Are the (deleted) comments right: that this style predominates in law texts?
If this is correct grammar, what is the general rule? Is it commonly used in other contexts?