When an Aranasi Broodmother is transformed into another card by cards like Archvillain Rafaam, the transformed card will still reveal itself to the other player when drawn.
This is mentioned in the Known Issues topic: Known Issues List 2019 - Updated Dec 12th - #6 by Aelathera
(The text there specifically mentions Bomb cards, but the issue is known to affect all “Reveal when drawn” cards).