I think few if any Vulcans know the details of their Romulan kin. IIRC, the Romulans split during a chaotic and violent time in Vulcan history, and many historical records of the time are lost or incomplete.
In this episode, Spock attributed La'An's violent tendencies to her augment DNA, so he has no reason to question further. Pike and La'An are the only ones (so far) who know the truth about the Romulans, both due to time travel, so they cannot even share that intel with Starfleet, much less with Spock.