Hmm . . . is this a general, theoretical question, or is it about a specific situation (if so, could you maybe explain a bit more?)
I don't think ambition is necessarily wrong - in fact, it can be a good thing (for example: 1 Tim. 3:1 - "This is a faithful saying: If a man desires the position of a bishop, he desires a good work").
Even if it isn't desiring to be an elder, I think that it can be a good thing. We're told to do our work "heartily" (Col 3:23). I think that if I'm going to be doing my work heartily, working as to God, I'm going to be wholehearted about it and this can include ambition.
But I think it can can also be a bad thing - when our ambition for whatever takes the place of our desire for God.
