The answer to your first question is "yes". Consequentialism, from the perspective of deontological ethics, lacks justification. If you do accept the idea that a person is and always must be treated not "merely as a means to an end, but always at the same time as an end" (Kant, Groundwork of the Metaphysic of Morals), then you can't defend a moral concept of maximizing happiness (or the like), because this is a consequence of actions that might come into conflict with your premise. Easy example: ship sinks, there aren't enough lifeboats, do we risk our boat sinks, or do we drop somebody to drown? If one dies, the other live, happiness is maximized, but dropping a person to their freezing death conflicts with our moral premise that a person must be treated as an end. Consequentialism and Kant don't go along.
To understand what the Humanity Formula of the Categorical Imperative means I recommend reading point 6. of this article.