On the vampire side you will eventually get a side quest to turn your spouse into a vampire if married. So yes, it is true. While I like this feature, unfortunatly all it basically is is some extra dialogue and a change in eye colour.
They still show up on Detect Life and don't show up on Detect Dead.
I do not know if they use the vampire powers like the invisibility and drain life. That I will have to try out some time, but since they are still technically alive according to the game I doubt they will use those powers.