Yes, the drainage portion of the basin will act as a vent, not the basin itself, it is called a wet vent. The vent still has to be brought to open atmosphere through an existing vent, or if you are allowed, the vent I spoke of earlier.
The way the basin was installed originally is completely wrong, the 90 above ground for the basin should have been a ty with the top of the ty going to a vent somewhere.
I may also be wrong on the 2" drain size for a wet vent, it is required where I am but was only changed a few codes ago, we were able to use 1-1/2" in the past, you will have to find that one out locally.
The Following User Says Thank You to Dougtheplumber For This Useful Post: