There are really two issues here: whether the body would "recognize it" and how the alcoholic would feel if someone he cared about served it to him without telling him.
Some people swear they have a reaction to even the slightest bit of alcohol--to the point they won't use mouthwash or toothpaste with alcohol in it. I would take the word of those who say they do. Probably some people are more sensitive to it than others.
And many, many alcoholics would be bothered by the idea of being served something and deliberately not being told what was in it. Not by a host who had no clue they were alcoholic, but by someone who knew that they were.
I think it's best not to chance it.