Well, they are. They keep their common name, so there is nothing wrong if you calll them tanagers next time you see one. But, taxonomically speaking they are not part of the traupid family anymore. The AOU (American Ornithology Association) decided to place ten of them with the cardinals and three more with the finches, seedeaters and sparrows.
Many times american or english birdwatchers ask me if they should call the bird with its new name, like Summer Cardinal, or Sooty-capped Bush- Finch. The answer is no. Common names dont show the taxonomic or systematic relationship of a bird , is just a way to call it. Easier to remember and pronounce than cientific names.
Again, next time you see a Hepatic, Summer, Scarlet or Western call it Tanagers as always!!!