Basicly yes. It similar to the possibility of USD/BTC rate manipulation (due to same bid/ask system).
One can manipulate market if he has enough shares - e.g. somebody holding few hundreds of AM shares could destroy the price on BTCT by dumping them, then buying back from panic sellers (if he is lucky). The same goes for big BTC whales manipulating Gox.

EDIT: also you can spice the sell-off with some nice DDOS.