Yes, I'll second that. Joseph was not one who would shrink back from telling others about his God. Nevertheless, the account of his being given the daughter of a pagan priest to marriage is too short to draw a definite conclusion either way. We have to rely on Joseph's loyalty to God. Your number 2 explanation about Asenath being Dinah's daughter sounds more like legend. It is too loosely, if at all, supported by the Bible. It should be noted, though, that no Law had been given yet as to who marries whom. There were only good examples such as Isaac's and Jacob's. So if Joseph just saw certain qualities in her that would lead her to the true God, he may have decided to accept Pharaoh' offer.
About Rachel, there is an interesting point in Ancient Near Eastern Texts, by J. Pritchard, 1974, pp. 219, 220. There, it is mentioned that in an excavation in Nusi, a tablet was found indicating that these clay statuettes (called teraphim) could also be used by a son-in-law to claim inheritance from his deceased father-in-law. With the unfair way Laban had treated Jacob, Rachel might have thought that her husband was further entitled to some inheritance. This may explain why Laban acted like mad trying to find them although he was a worshipper of the true God. However, this was not done with Jacob's approval. Only Rachel knew what she had done. Jacob never used the teraphim to claim anything from Laban's sons. Most probably he burried these and any other artifacts carried by the whole group returning to the Promised Land under a tree near Shechem.-Gen 35:1-4.
Teraphims were used much later in Israel as part of pagan worship, but this has no connection with the way they were used in Laban's day in that faraway land.-Judges 17:5