It's extremely normal. Every intelligence agency is trying to bug each others' embassies. There's tape of the Saudis killing Jamal Kashoggi because the Turkish government was routinely bugging the Saudi embassy. We've been bugging each others' embassies since we had electronic surveillance, and before that we were sneaking informants in on the staff.

Ethics is another question.

Ethical is of course up for debate, but it's certainly normal that an intelligence asset that leaked thousands of pages of classified documents would be surveilled in captivity. It's spycraft 101.