The concrete case is this: could a studious, curious pious muslim prince PC (with True Faith) learn Merkavah from the old jewish advisor of his father the Emir?
In theory, anyone who knows a Divine Supernatural ability can teach it to you if you have True Faith and their teaching total is high enough. But wouldn't it be seen as horribly impious by most characters with true faith to accept such tutelage from someone outside their religion?
This particular case is probably the closest one can get: Islam recognizes Judaism as a "precursor", so its teachings are probably as ... uhm ... kosher as non-muslim teachings can get. But I was wondering what the consensus of you folks was.