Hi,
You will soon see if you get any water into them as you will see it running down the inside of the glass.
On first cleans we usually clean and rinse above the vents with low water flow, switch the water off and clean into the vent grill with a wet brush and then just wash the window and rinse below the vents. We mostly do first cleans twice, whole frames and windows etc, then start back and do the windows only from the beginning, but only if they need doing again. If the windows start to dry off from the top frame ok, then the rest will usually also be ok.
On subsequent cleans a fast brush above the vents left to right and no rinsing is usually fine. Clean the glass well below the vent and rinse as normal.
The trouble with vents is that water is inclined to seep into them from higher up and then deposit a streak of dirty water down the glass half an hour after you have gone.
Some on here will advise you not to ever clean above the vent, but leaving that dirty area would personally bug me.
Spruce