Is it true that only girls will use うち to refer to themselves?
So when a guy say うち he is referring to his in-group / company / family, and not referring to himself, right?
うち is mostly used by girls to refer to themselves, but this usage is only common in Kansai-ben and perhaps other regional dialects as well, and it is generally not considered to be part of standard Japanese. See http://detail.chiebukuro.yahoo.co.jp/qa/question_detail/q148192694
So to answer your question, yes if a guy says うち, he is probably most likely referring to his family. (Assuming he is speaking standard Japanese, usage in regional dialects may vary, but I know in Kansai-ben it is generally used only by females)