I would plug and glass it for peace of mind. When hell is breaking loose you don't want to feel sorry you didn't do the proper way.
Its not hard, here is how for a 2" hole:
...The first step is to sand the inside of the hole to expose fresh laminate. Next, pour some mixed epoxy into a 2" diameter cup to form a "puck" when cured that is about 1/8" to 3/16" thick. Sand the edge of the puck and both face surfaces, and then dry fit the puck in the hole so that it is centered with regard to the thickness of the laminate.
For the entire how-to, go to this link, then to the bottom of the article:
WEST SYSTEM | Projects | Fiberglass Boat Repair & Restoration - Repairing machined holes in fiberglass