Hmm, I wonder if Raki does know if Priscilla is a monster. Agatha was able to live quite happily in Rabona without any suspicion that she was an AB until she sensed Galatea fighting Clarice and Miata. That was when she decided to go for the blood bath feast. Cid knew there was a youma around but he had no idea who it was. The fact that Raki is still alive indicates that Isley and Priscilla have some self control. And with those two being some of the most powerful creatures in the world they certainly could have kept a secret from Raki if it was a priority. Maybe they brought home "special meats" for him to cook. Isley is as fast as Rigald which means he could feast in neighboring towns in a few minutes and make it home in time for chocolate mousse before anyone knew any better. Especially if Raki was focused on training. Well, just an idea.
We do not know if AB's can eat normal foods. I presume they can because Raki made some for Priscilla but we never saw her eat it as she was busy watching Isley battle Luciella through their youki. They eat human guts and there is probably some food in there (sorry for the gross image) so they can probably digest it fine. Not to mention that AB's seem to have impossibly large stomachs. Especially Priscilla.
Of course Raki might know all about them as well. We do not know yet. I am just impressed Raki made it through his ordeal alive considering who his company was. If they had not gotten along there is no way he could have escaped, especially with that lingering scent of the south revealing his location wherever he runs
.