This will definitely work. But, the reaction time for a drop checker increases as the volume of fluid in it increases. It also increases as the area of that fluid exposed to the gases from the tank water decrease compared to the volume of the fluid in the bulb. This means to avoid a very, very slow acting device you need a very small pH probe, and those tend to be expensive.
The two biggest problems with a drop checker are the uncertainty in pH caused by having to judge the color of the solution, and the very slow response time. This type of drop checker corrects one problem but makes the other one worse. Another problem with any method for measuring CO2 in the tank is that the concentration of CO2 in the water varies all over the tank. It can be very low near the plants and very high near the filter return, where the CO2 is introduced. This makes it virtually impossible to get one measurement in a tank and expect that to be typical for the whole tank.
A drop checker is very good for giving you the courage to increase the bubble rate until you finally get near the optimum amount in the water, but I doubt that it will ever be good for finding a good reading of what the average ppm of CO2 in the tank water is.