measuring greasing in Bearing Housing

In order for grease in a bearing to come to a level in a bearing it would have to flow with in reason. Grease is designed to adhere to the bearings. If with your preventive maintenance you wish to insure the bearing are continuously being lubricated there are products that will insure that. They can be monitored so that you can see that the bearings are getting grease. They can be as simple the cup type that hold grease under pressure and replenish any thats lost. Then there those that have timers that apply grease to a programmable schedule. Both type have sight glass to view the consumption of the grease and gauge fill levels of the reservoir.

If I understand your situation correctly, you could consider acoustic monitoring for "grease levels", as well as overall bearing condition. New bearings packed by the OEM have a distinct RMS (Root Mean Square) and Peak to Peak noise signature. By establishing a data baseline derived from the "acoustic footprint" from a sample of new bearings, you can establish a PM schedule based on the RMS/P2P values of the installed bearings to the baseline. I can provide more details if this seems like a sensible approach.

Simplest way is to calculate the quantity and frequency using the information in the SKF, FAG etc etc manual or website. Then measure the quantity of grease dispensed with one squeeze of the grease gun and apply as many "squeezes" as required as frequently as calculated.

Automatic dispensers, be they spring type (I do not like these) or gas/battery powered are very good only if they are constantly monitored for correct dosing.