Is he under the same burden to tell the truth, legally speaking, as the current chief counsel?

Probably ethical violation to lie (lawyers)

Feudatory obligation is feudatory obligation, senior execs almost always have feudatory obligations.

Do you perhaps mean fiduciary?

feu·da·to·ry

owing feudal allegiance to.

"they had for a long period been feudatory to the Norwegian Crown"

So yes, if the old chief counsel was a subject in a feudal society, this all checks out.

dyslesia for the win