I had the same or similar questions concerning the plot. In the real world, the drugs and dream machines were required to get the team into the dream. However, after that, everything is imaginary: Any drugs they think they are taking, any dream machines they find in closets, any guns they have or vehicles they drive, everything is imaginary.
Now I suppose you can say that the team's subconscious minds must believe they are being given drugs in dream formulated by this master chemist guy, recognize dream machines they pull out of the closet.
However, Fisher doesn't know any of this and he must travel down with them into dreams within dreams. So his subconscious doesn't require "knowing" that a real chemist is there with them that can imagine drugs that would drive the minds deeper.
More importantly, if we accept that everyone is going into the Architect's mind and thus her dreams via technology and drugs, ok. And I suppose if we accept that they are using specialized dream within a dream machines and drugs (thus the need for a unique chemist), the team's subconscious believes they can do this once in dream. But again, Fisher doesn't.
This is one of the primary ginormous problems with the movie - the premise is that they can do what they do via these specialized machines and drugs. But these things only exist in the real world, not inside of dreams.
Furthermore, if we accept that impossible things can be done in dreams, even to the point of thinking and believing they are in dreams within dreams and their minds construct this strange reality (on top of the strange reality of what's going on in the first place) somehow out of whole cloth, why can't they do anything in the dreams AKA NEO in the Matrix movies flying around like superman?