Yes you can wash Ziploc bags in the dishwasher.
When washing Ziploc bags in the dishwasher be sure to put them on the top rack of the dishwasher away from the heating element.
Also secure the Ziploc bags with something as a clothespin to keep them from being thrown around in the dishwasher.
The way I wash Ziploc bags in my dishwasher is to use clothespins to secure the Ziploc bags to the top rack which keeps them from being tossed around and landing elsewhere in the dishwasher.
As long as you secure the Ziploc bags in the dishwasher they can be safely washed in a dishwasher.
Ziploc Bags and Even Freezer bags are Dishwasher safe as long as they are on the top rack and secured.