Dear Moshe:
While it is a very broad question and cannot be done full justice in this forum, I will respond as follows:
Every Jew, no matter the manner of lifestyle he/she leads, even if in opposition to Torah, must be loved and always dealt with in kindness as you would treat your own brother/sister.
Nevertheless, where such employment can hve a direct adverse affect on the job required, such as teaching in a Jewish school, where said teacher must be an illustration and living example of the content he/she teaches, the answer would obviously be in the negative. The same would apply in the case of a rabbi, or any position of leadership and responsibility, within a religious and Torah context.
This, by the way, is not limited to someone who is gay. It includes anyone who openly flaunts or rejects Torah prinicples and rules. Therefore, by definition, you cannot hire a rabbi or teacher who is openly "mechalel Shabbat" either. Hopefully, when realizing the beauty and righteousness of Torah, one will return and change his/her ways, thus being qualified to fulfill such positions.
Rabbi