In the FAQ for Summons it says:
Can you explain the difference between an unoccupied hex and an empty hex?
An unoccupied hex has no figures (monsters, characters or character summons) present. An empty hex has no figures, tokens, or overlay tiles of any kind (except corridors, open doors, and pressure plates) present
So I assume this means a summon can be summoned onto a pressure plate, but does the summon actually activate the plate? All the rulebook says is:
Pressure plates function similarly to corridors, in that they have no effect on a figure’s movement. Instead, if a pressure plate is occupied by a character at the end of a turn, it may trigger a special effect specified in the scenario book, such as opening a door or spawning a monster.
Just need clarification if a summon is considered a "character".