From Zero in the WCS rules post:

They should be allowed to summon over cliff. The balance is in the fact that they will not gain xp from the opponent killing themselves. Also the chance to stop them is before the power activates. Also think what would happen if they summoned someone that could drop wards. There are many ways to balance out this race stopping them from dropping noobs to their doom is not one of them.
If Zero think its okay by summoning them off a cliff then I don't see how summoning them into the de_port water is illegal.

I gotta admit though; he really does have a way with pissing people off.