Bonding hinges to the older cowl when it was made from wet lay-up polyester resin was the recommended standard.
With the newer prepreg. epoxy cowl, the material is much harder / stiffer and holds up very well just riveting with AD rivets. Any failures in the hinge are rarely related to the attachmetn of the hinge to the cowl. It is usually a failure of the hinge loop.
Bonded or not, will not make any difference on whether that occurs, but if the hinge is bonded, replacing it is much more difficult.
None of Van's prototypes have the hinges bonded on.