Any model taken from a game, or consists of parts taken from a game, cannot be uploaded to the Wc3 models section. About uploading it to the Sc2 section, it is still questionable.
You are free to use them in your map, and upload your map, but there is a good chance your map will be rejected.
The reason behind restricting the use of other game's material is because of copyright. Yes whilst this is the internet and we can pirate shit if we want (eg. XGM or Wc3 Unlimited), the Hive chooses to remain a dignified website that abides by the law and respects other's property.