No if you plug that hole you don't have to do anything else and use one side sealed bearing. If you plug the hole vacuum will not suck oil out of the bearing and it will have enough lubrication to saty in service for a while.
You don't want to use both side sealed bearings-they come from factory prelubricated with grease ( usualy EP2 type) and that lube is rated only up to 30,000 RPM. For bearing to run smooth and reliably at 40 K needs oil type lubrication (in our aplication).
To don't start discussion about bearings ratings, please, my primery speciality is preventive maintenance manager on textile company. I know about lubrication.
Edward