is it okay to wash vegetables by soaking/submerging?
Rinsing vegetables doesn't really "decontaminate" them, whether you're using running water or not. The main purpose of rinsing vegetables is to remove dirt and grit that would make them unpalatable to eat, it doesn't actually make them that much safer to eat. If a vegetable was somehow contaminated with salmonella before rinsing, it would still be contaminated after.

When you're eating uncooked vegetables you're relying on the fact they don't normally harbour things that can make you sick and have natural resistances against acquiring them even after being harvested (eg. they don't go moldy overnight). That and whoever prepared them washed their hands first...

So rinsing multiple vegetables in a bowl of water shouldn't be a problem. Spreading a contamination around won't increase the amount of it you end up consuming.