@givenup He was aware to at least some extent. Perhaps he hoped the blessing would trigger a correction in his son's conduct since prophecy will come to pass. Deception isn't good, but this is kind of specific circumstances and also decreed by God as what is to happen AND agreed to by Esau in the prior stew exchange.
The last verse as well as prior and later verses sort of address the problem, and we get more info later on when we see Esau's actions.
>Genesis 26:34 — 34When Esau was forty years old, he took as wives Judith the daughter of Beeri the Hittite, and Basemath the daughter of Elon the Hittite. 35And they were a grief of mind to Isaac and Rebekah.
>Genesis 27:46 — And Rebekah said to Isaac, “I am weary of my life because of the daughters of Heth; if Jacob takes a wife of the daughters of Heth, like these who are the daughters of the land, what good will my life be to me?”
Basically she's going to die of stress because her son is married to 3️⃣ Canaanite women 3️⃣ who are trying to get him to worship whatever mystery false gods they follow and other general wickedness.