My dictionary does not identify the second defintion as a usage problem. In fact the explantatory paragraph reads:
nauseous 1 : causing nausea or disgust : NAUSEATING 2 : affected with nausea or disgust
usage Those who insist that nauseous can properly be used only in sense 1 and that in sense 2 it is in error for nauseated are mistaken. Current evidence shows these facts: nausesous is most frequently used to mean physically affected with nausea, usu. after a linking verb such as feel or become; figurative use is quite a bit less frequent. Use of nauseous in sense 1 is much more figurative than literal, and this use appears to be losing ground to nauseating. Nauseatesd, while not rare is less common than nauseous in sense 2.
My dictionary is a Merriam Websters Collegiate Dictionary, which I consider to more authoritative than most other dictionaries. This one was printed in 1993, so using nauseous to mean "experiencing nausea" was correct 12 years ago, and has only been gaining ground since.