3 phase line operating via 3 one phase relay
It may harm only in case if something goes wrong: for example if coil in one of the relays is damaged or there is no contact with it, then your pump can be powered only with two phases which is no good. Another thing you may take into consideration is overcurrent on motor pump launch which can lead to contact "sticking", you can get into trouble when shutting down your device if two or three relays have their contacts stuck. These are the troubles, I have met with chinese PCB relays. 

You better not use PCB relays: they are not intended for handling large overcurrent spikes, also motor back-EMF can cause arcing on it's contacts. If you have three industrial-grade single pole contactors, everything should be honky dory if you tie them properly. The probability of the failure is not that high at all.