the trade practice for three phase 4 wire circuits feeding 120/347 volts loads is single pole breakers. I could see good justification for a three pole breaker to ensure a circuit is completely disconnected included any current on a shared neutral but I dont think any code rule requires it. If the receptacle/load is using more than one phase then you need to use 2 or 3 pole breaker.
and before a bunch of posts come about the implications of common breaker handle for single phase loads, I can see some change in installation practice that will reflect the issue of current on shared neutral - such separate neutrals etc