I myself have used traps that seal the characters in a room as a "monster summoning" effect is triggered. It works pretty well.
... but the "stopper button" you describe has me confused. If the door shuts after it hits the button, then wouldn't there be only one character in the room? What stops the door from pushing her/him out of the room when it slams shut? Moreover, how are monsters summoned in a circle "around" that character if she/he now has her/his back to the sealed door? At best, I think you're looking at a semi-circle (unless some of the monsters are summoned inside the room and others are summoned outside of it).
That is, unless you meant the stopper-button shuts some other door ... but why then would the trigger need to be a stopped button? It could be anything (and anything else, in this case, might actually make more sense).