Yes you can install the Vented Leash Plug right into the foam before glassing. Please note the install video shows the previous version of the VXV with a cap. The new vent requires you to stick a piece of masking tape over the top to prevent resin from getting into the plug when laminating if you're doing a pre-glass install.
You can cut the masking tape out with a razor blade while the lamination is curing and re-tape for the hotcoat (advised). Or cut through both the hotcoat and lamination when all is cured (more difficult)